From 26a029d407be480d791972afb5975cf62c9360a6 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Fri, 19 Apr 2024 02:47:55 +0200
Subject: Adding upstream version 124.0.1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 .../soft-navigation-heuristics/back.tentative.html |  36 +++
 .../click-event-bubbles.tentative.html             |  28 ++
 .../tests/soft-navigation-heuristics/disabled.html |  31 ++
 .../dropped-entries.tentative.html                 |  42 +++
 .../first-interaction-not-softnav.tentative.html   |  36 +++
 .../soft-navigation-heuristics/hash.tentative.html |  29 ++
 ...-before-detection-second-softnav.tentative.html |  60 ++++
 .../image-lcp-before-detection.tentative.html      |  54 ++++
 ...cp-followed-by-image-softnav-lcp.tentative.html |  32 ++
 ...lcp-followed-by-text-softnav-lcp.tentative.html |  31 ++
 ...llowed-by-two-image-softnavs-lcp.tentative.html |  75 +++++
 .../innertext.tentative.html                       |  32 ++
 ...teraction-with-paint-before-back.tentative.html |  76 +++++
 ...load-classic-script-history-push.tentative.html |  31 ++
 .../load-module-script-history-push.tentative.html |  32 ++
 .../multiple-nested-events.tentative.html          |  40 +++
 .../multiple-paint-entries-buffered.tentative.html |  43 +++
 .../soft-navigation-heuristics/navigate-child.html |  30 ++
 ...tion-api-after-transition-commit.tentative.html |  28 ++
 .../navigation-api-back.tentative.html             |  45 +++
 .../navigation-api-forward.tentative.html          |  48 +++
 .../navigation-api-hash.tentative.html             |  28 ++
 .../navigation-api-preventDefault.tentative.html   |  35 ++
 .../navigation-api-rejected.tentative.html         |  28 ++
 .../navigation-api-traverseto.tentative.html       |  49 +++
 .../navigation-api-view-transition.tentative.html  |  54 ++++
 .../navigation-api.tentative.html                  |  26 ++
 .../popstate-multiple-backs.tentative.html         |  64 ++++
 .../popstate.tentative.html                        |  50 +++
 .../replacestate-null-then-push.tentative.html     |  34 ++
 .../replacestate.tentative.html                    |  28 ++
 .../resources/empty.html                           |   2 +
 .../resources/history_push.js                      |   1 +
 .../resources/soft-navigation-helper.js            | 356 +++++++++++++++++++++
 .../second-interaction-not-softnav.tentative.html  |  35 ++
 ...gation-detection-main-descendent.tentative.html |  30 ++
 ...ft-navigation-detection-non-main.tentative.html |  25 ++
 ...etection-web-component-lifecycle.tentative.html |  46 +++
 .../soft-navigation-detection.tentative.html       |  26 ++
 .../soft-navigation-no-url.tentative.html          |  31 ++
 ...r-lcp-paint-larger-than-viewport.tentative.html |  70 ++++
 .../softnav-after-lcp-paint.tentative.html         |  42 +++
 .../softnav-before-lcp-paint.tentative.html        |  52 +++
 ...nav-between-lcp-render-and-paint.tentative.html |  36 +++
 .../supported-entry-types.tentative.html           |  15 +
 ...-before-detection-second-softnav.tentative.html |  62 ++++
 .../text-lcp-before-detection.tentative.html       |  55 ++++
 ...llowed-by-anim-image-softnav-lcp.tentative.html |  32 ++
 ...cp-followed-by-image-softnav-lcp.tentative.html |  31 ++
 ...lcp-followed-by-text-softnav-lcp.tentative.html |  34 ++
 .../visited-link.tentative.html                    |  48 +++
 51 files changed, 2284 insertions(+)
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/back.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/click-event-bubbles.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/disabled.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/dropped-entries.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/first-interaction-not-softnav.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/hash.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/image-lcp-before-detection-second-softnav.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/image-lcp-before-detection.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-image-softnav-lcp.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-text-softnav-lcp.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-two-image-softnavs-lcp.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/innertext.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/interaction-with-paint-before-back.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/load-classic-script-history-push.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/load-module-script-history-push.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/multiple-nested-events.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/multiple-paint-entries-buffered.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/navigate-child.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/navigation-api-after-transition-commit.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/navigation-api-back.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/navigation-api-forward.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/navigation-api-hash.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/navigation-api-preventDefault.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/navigation-api-rejected.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/navigation-api-traverseto.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/navigation-api-view-transition.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/navigation-api.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/popstate-multiple-backs.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/popstate.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/replacestate-null-then-push.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/replacestate.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/resources/empty.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/resources/history_push.js
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/resources/soft-navigation-helper.js
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/second-interaction-not-softnav.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-main-descendent.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-non-main.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-web-component-lifecycle.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-no-url.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/softnav-after-lcp-paint-larger-than-viewport.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/softnav-after-lcp-paint.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/softnav-before-lcp-paint.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/softnav-between-lcp-render-and-paint.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/supported-entry-types.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/text-lcp-before-detection-second-softnav.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/text-lcp-before-detection.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-anim-image-softnav-lcp.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-image-softnav-lcp.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-text-softnav-lcp.tentative.html
 create mode 100644 testing/web-platform/tests/soft-navigation-heuristics/visited-link.tentative.html

(limited to 'testing/web-platform/tests/soft-navigation-heuristics')

diff --git a/testing/web-platform/tests/soft-navigation-heuristics/back.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/back.tentative.html
new file mode 100644
index 0000000000..349eaf465c
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/back.tentative.html
@@ -0,0 +1,36 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link>Click me!</a>
+    </div>
+  </main>
+  <script>
+    // Push state a couple of times
+    history.pushState({}, "", "foobar.html");
+    history.pushState({}, "", "anotherOne.html");
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: () => {
+        addTextToDivOnMain();
+      },
+      link: link,
+      pushState: url=>{history.back()},
+      test: "`history.back() properly works with SoftNavigationHeuristics"});
+  </script>
+</body>
+</html>
+
+
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/click-event-bubbles.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/click-event-bubbles.tentative.html
new file mode 100644
index 0000000000..ee9d1e1233
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/click-event-bubbles.tentative.html
@@ -0,0 +1,28 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    // Adding a noop event that the "click" would bubble to.
+    document.getElementById("main").addEventListener("click", () => {});
+
+    testSoftNavigation({
+      addContent: () => {
+        addTextParagraphToMain("Lorem Ipsum");
+      },
+      link: link,
+      test: "Ensure event bubbling works well with soft navigations."});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/disabled.html b/testing/web-platform/tests/soft-navigation-heuristics/disabled.html
new file mode 100644
index 0000000000..b53c2f7012
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/disabled.html
@@ -0,0 +1,31 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+    <script>
+    const link = document.getElementById("link");
+    testSoftNavigationNotDetected({
+      eventHandler: url => {
+        addTextToDivOnMain();
+        history.pushState({}, '', 'foobar.html');
+      },
+      link: link,
+      eventName: "click",
+      eventTarget: link,
+      testName: "Test that a soft navigation is not detected when the feature "
+                + "is disabled"});
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/dropped-entries.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/dropped-entries.tentative.html
new file mode 100644
index 0000000000..d27ad452be
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/dropped-entries.tentative.html
@@ -0,0 +1,42 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<meta name="timeout" content="long">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+
+    testSoftNavigation({
+      addContent: async () => {
+        await addImageToMain('green-16x16.png');
+      },
+      link: link,
+      clicks: 52,
+      extraValidations: async (entries, options)=>{
+        if (!performance.softNavPaintMetricsSupported) {
+          return;
+        }
+        const [paint_entries, paint_options] = await new Promise(resolve => {
+          new PerformanceObserver((list, obs, options) =>
+            resolve([list.getEntries(), options])).observe(
+            {type: 'paint', buffered: true});
+          });
+        assert_equals(options['droppedEntriesCount'], 2);
+        assert_equals(paint_options['droppedEntriesCount'], 4);
+      },
+      test: "Test that a soft navigation entries get dropped when buffer limits"
+        + " get exceeded."});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/first-interaction-not-softnav.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/first-interaction-not-softnav.tentative.html
new file mode 100644
index 0000000000..e026202183
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/first-interaction-not-softnav.tentative.html
@@ -0,0 +1,36 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <p><a id=firstlink>Click me!</a></p>
+  <p><a id=secondlink>Then click me!</a></p>
+  </main>
+  <script>
+    (async () => {
+    if (test_driver) {
+        const firstlink = document.getElementById("firstlink");
+        const clickPromise = new Promise(r => {
+          firstlink.addEventListener("click", r);
+        });
+        test_driver.click(firstlink);
+        await clickPromise;
+      }
+    })();
+    const secondlink = document.getElementById("secondlink");
+    testSoftNavigation({
+      addContent: () => {
+        addImageToMain();
+      },
+      link: secondlink,
+      test: "first interaction in the middle of a soft navigation"});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/hash.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/hash.tentative.html
new file mode 100644
index 0000000000..3a8419c71d
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/hash.tentative.html
@@ -0,0 +1,29 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect hashchange event.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link>Click me!</a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: () => {
+        addTextToDivOnMain();
+      },
+      link: link,
+      pushState: (url)=>{location.hash=url;},
+      test: "Location hash changes properly works with SoftNavigationHeuristics"});
+  </script>
+</body>
+</html>
\ No newline at end of file
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-before-detection-second-softnav.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-before-detection-second-softnav.tentative.html
new file mode 100644
index 0000000000..4d26bb9269
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-before-detection-second-softnav.tentative.html
@@ -0,0 +1,60 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img src="/images/lcp-256x256.png" id="img"></a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    let first_lcp_painted;
+    let second_lcp_painted;
+    (async () => {
+      await new Promise(r => { first_lcp_painted = r; });
+      addImageToMain("lcp-133x106.png", "no_lcp");
+      (new PerformanceObserver(second_lcp_painted)).observe({type: "element"});
+    })();
+    testSoftNavigation({
+      pushState: null,
+      clicks: 2,
+      addContent: async () => {
+        // Add an LCP element.
+        await new Promise(resolve => {
+          addImageToMain("lcp-100x50.png", "first_lcp" + counter);
+          (new PerformanceObserver(resolve)).observe({type: "element"});
+        });
+        if(counter) {
+          first_lcp_painted();
+          // Wait for the unrelated LCP to be painted.
+          await new Promise(r => { second_lcp_painted = r; });
+        }
+        const url = URL + "?" + counter;
+        history.pushState({}, '', url);
+      },
+      link: link,
+      validate: async () => {
+        const lcps = await getLcpEntries();
+        const ref_counter = counter-1;
+        assert_equals(lcps.length, 2 + ref_counter, "Got 2 LCP entries");
+        assert_equals(lcps[lcps.length - 1].id, "first_lcp" + ref_counter,
+                      "Got the first LCP");
+      },
+      test: "Second soft navigation image LCP discovered between user " +
+            "interaction and soft navigation detection are properly " +
+            "reported, while unrelated LCPs are ignored during that time. " +
+            "As a side effect, we also test element timing."});
+  </script>
+</body>
+</html>
+
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-before-detection.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-before-detection.tentative.html
new file mode 100644
index 0000000000..0de675d372
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-before-detection.tentative.html
@@ -0,0 +1,54 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img src="/images/lcp-256x256.png" id="img"></a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    let first_lcp_painted;
+    let second_lcp_painted;
+    (async () => {
+      await new Promise(r => { first_lcp_painted = r; });
+      addImageToMain("lcp-133x106.png", "no_lcp");
+      (new PerformanceObserver(second_lcp_painted)).observe({type: "element"});
+    })();
+    testSoftNavigation({
+      pushState: null,
+      addContent: async () => {
+        // Add an LCP element.
+        await new Promise(resolve => {
+          addImageToMain("lcp-100x50.png", "first_lcp");
+          (new PerformanceObserver(resolve)).observe({type: "element"});
+        });
+        first_lcp_painted();
+        // Wait for the unrelated LCP to be painted.
+        await new Promise(r => { second_lcp_painted = r; });
+        const url = URL + "?" + counter;
+        history.pushState({}, '', url);
+      },
+      link: link,
+      validate: async () => {
+        const lcps = await getLcpEntries();
+        assert_equals(lcps.length, 2, "Got 2 LCP entries");
+        assert_equals(lcps[lcps.length - 1].id, "first_lcp", "Got the first LCP");
+      },
+      test: "Image LCP discovered between user interaction and soft " +
+            "navigation detection are properly reported, while unrelated " +
+            "LCPs are ignored during that time. As a side effect, we also " +
+            "test element timing."});
+  </script>
+</body>
+</html>
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-image-softnav-lcp.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-image-softnav-lcp.tentative.html
new file mode 100644
index 0000000000..7a2018d20e
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-image-softnav-lcp.tentative.html
@@ -0,0 +1,32 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img src="/images/lcp-256x256.png"></a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        const main = document.getElementById("main");
+        main.removeChild(document.getElementsByTagName("div")[0]);
+        await addImageToMain();
+      },
+      link: link,
+      test: "Test that an image LCP followup by a smaller soft navigation image LCP"
+        + " properly queues an LCP entry"});
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-text-softnav-lcp.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-text-softnav-lcp.tentative.html
new file mode 100644
index 0000000000..501d1c5fb6
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-text-softnav-lcp.tentative.html
@@ -0,0 +1,31 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img src="/images/lcp-256x256.png"></a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: () => {
+        addTextToDivOnMain();
+      },
+      link: link,
+      test: "Test that an image LCP followup by a smaller soft navigation text LCP"
+        + " properly queues an LCP entry"});
+  </script>
+</body>
+</html>
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-two-image-softnavs-lcp.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-two-image-softnavs-lcp.tentative.html
new file mode 100644
index 0000000000..66a9e5136f
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/image-lcp-followed-by-two-image-softnavs-lcp.tentative.html
@@ -0,0 +1,75 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img src="/images/lcp-256x256.png"></a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+
+    promise_test(async t => {
+      validatePaintEntries('first-contentful-paint', 1);
+      validatePaintEntries('first-paint', 1);
+      const preClickLcp = await getLcpEntries();
+      setEvent(t, link, /*pushState=*/url=>history.pushState({}, '', url),
+        /*addContent=*/async () => await addImageToMain(), /*pushUrl=*/true,
+        /*eventType=*/"click");
+
+      const first_click_paint_promise = waitOnPaintEntriesPromise();
+
+      interact(link);
+      await new Promise(resolve => {
+        (new PerformanceObserver(resolve)).observe({
+          type: 'soft-navigation'
+        });
+      });
+      assert_equals(
+          document.softNavigations, 1,
+          'One Soft Navigation detected');
+
+      await first_click_paint_promise;
+      const postClickLcp = await getLcpEntries();
+      assert_greater_than(
+          postClickLcp.length, preClickLcp.length,
+          'Soft navigation should have triggered at least an LCP entry');
+      assert_less_than(
+          postClickLcp[postClickLcp.length - 1].size,
+          preClickLcp[preClickLcp.length - 1].size,
+          'Soft navigation LCP element should have a smaller size than the hard'
+              + ' navigation LCP element');
+
+      const second_click_paint_promise = waitOnPaintEntriesPromise();
+      const preClickLcp2 = await getLcpEntries();
+      interact(link);
+      await new Promise(resolve => {
+        (new PerformanceObserver(() => resolve())).observe({
+          type: 'soft-navigation'
+        });
+      });
+      assert_equals(
+          document.softNavigations, 2,
+          'Two Soft Navigations detected');
+
+      await second_click_paint_promise;
+      const postClickLcp2 = await getLcpEntries();
+      assert_equals(postClickLcp2.length, 3, 'We expected 3 LCP entries at this point');
+      assert_greater_than(
+          postClickLcp2.length, preClickLcp2.length,
+          'Soft navigation should have triggered at least an LCP entry');
+    }, "Multiple soft navigations get FP, FCP and LCP for each one");
+  </script>
+</body>
+</html>
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/innertext.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/innertext.tentative.html
new file mode 100644
index 0000000000..d40b604792
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/innertext.tentative.html
@@ -0,0 +1,32 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  <!-- This test fails if the paragraph below already has content. The reason
+       is that secondary paints are not being properly recorded, and hence don't
+       count for soft navigation heuristics. -->
+  <p id="softnav-content"></p>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        document.getElementById("softnav-content").innerText =
+          "Lorem Ipsum dolor sit amet";
+      },
+      link: link,
+      test: "Soft navigation when only innerText was modified"});
+  </script>
+</body>
+</html>
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/interaction-with-paint-before-back.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/interaction-with-paint-before-back.tentative.html
new file mode 100644
index 0000000000..b587411991
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/interaction-with-paint-before-back.tentative.html
@@ -0,0 +1,76 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img src="/images/lcp-256x256.png" id="img"></a>
+      <a id=not_nav><img src="/images/lcp-16x16.png"></a>
+    </div>
+  </main>
+  <script>
+    // Push state a couple of times
+    history.pushState({}, "", "foobar.html");
+    history.pushState({}, "", "anotherOne.html");
+
+    (async () => {
+      const link = document.getElementById("link");
+      // Trigger a user interaction that doesn't result in a soft navigation, but
+      // does paint.
+      await (async () => {
+        const not_nav = document.getElementById("not_nav");
+        let non_soft_nav_click;
+        const non_soft_nav_click_promise =
+          new Promise(r => { non_soft_nav_click = r; });
+        not_nav.addEventListener("click", () => {
+          addImageToMain("lcp-133x106.png", "not_soft_nav_image");
+          (new PerformanceObserver(non_soft_nav_click)).observe({type: "element"});
+        });
+        if (test_driver) {
+          test_driver.click(not_nav);
+        }
+        await non_soft_nav_click_promise;
+      })();
+      const url = URL + "?" + counter;
+      link.addEventListener("click", () => {
+        // Add an LCP element.
+        const img = new Image();
+        img.src = '/images/lcp-100x500.png' + "?" + Math.random();
+        document.getElementById("main").appendChild(img);
+        history.back();
+      });
+      promise_test(async t => {
+        if (test_driver) {
+          test_driver.click(link);
+        }
+        await waitOnSoftNav();
+        assert_equals(
+            document.softNavigations, 1,
+            'Single Soft Navigation detected');
+        const [entries, options] = await new Promise(resolve => {
+          (new PerformanceObserver((list, obs, options) => resolve(
+            [list.getEntries(), options]))).observe(
+            {type: 'soft-navigation', buffered: true});
+          });
+
+        assert_equals(entries.length, 1,
+                      "Performance observer got an entry");
+      }, "Ensure that soft navigation entry emitted through a synchronous " +
+         "event that modified DOM and committed a same document navigation, " +
+         "and that was preceded by a user intreaction that resulted in a " +
+         "contentful paint is properly detected.");
+    })();
+  </script>
+</body>
+</html>
+
+
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/load-classic-script-history-push.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/load-classic-script-history-push.tentative.html
new file mode 100644
index 0000000000..4e375b2164
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/load-classic-script-history-push.tentative.html
@@ -0,0 +1,31 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect a soft navigation triggered by an external classic script.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        await addImageToMain();
+      },
+      link: link,
+      pushState: async (url) => {
+        const script = document.createElement("script");
+        script.src = "resources/history_push.js";
+        document.body.appendChild(script);
+      },
+      test: "Detect a soft navigation triggered from external classic script"});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/load-module-script-history-push.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/load-module-script-history-push.tentative.html
new file mode 100644
index 0000000000..e82cd13f4a
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/load-module-script-history-push.tentative.html
@@ -0,0 +1,32 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect a soft navigation triggered by an external module script.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        await addImageToMain();
+      },
+      link: link,
+      pushState: async (url) => {
+        const script = document.createElement("script");
+        script.src = "resources/history_push.js";
+        script.type = "module";
+        document.body.appendChild(script);
+      },
+      test: "Detect a soft navigation triggered from external module script"});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/multiple-nested-events.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/multiple-nested-events.tentative.html
new file mode 100644
index 0000000000..e51841865d
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/multiple-nested-events.tentative.html
@@ -0,0 +1,40 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+    <script>
+    const link = document.getElementById("link");
+    let should_navigate = true;
+    navigation.addEventListener("navigate", () => {
+      if (should_navigate) {
+        // It's the last sync navigation that determines the soft nav URL.
+        history.pushState({}, '', 'foobar.html');
+        should_navigate = false;
+      }
+    });
+    testSoftNavigation({
+      eventPrepWork: url => {
+        addTextToDivOnMain();
+        history.pushState({}, '', 'foobar1.html');
+        // Here we're bypassing the regular test's event logic, as this test is
+        // fully sync.
+        return false;
+      },
+      link: link,
+      eventName: "click",
+      eventTarget: link,
+      testName: "Test multiple nested navigate events"});
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/multiple-paint-entries-buffered.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/multiple-paint-entries-buffered.tentative.html
new file mode 100644
index 0000000000..dbb945a0a8
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/multiple-paint-entries-buffered.tentative.html
@@ -0,0 +1,43 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<meta name="timeout" content="long">
+<title>Detect multiple soft navigations and ensure they buffer paint entries.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+
+    testSoftNavigation({
+      addContent: async () => {
+        await addImageToMain();
+      },
+      link: link,
+      clicks: 4,
+      extraValidations: async (entries, options)=>{
+        if (!performance.softNavPaintMetricsSupported) {
+          return;
+        }
+        const paint_entries = await new Promise(resolve => {
+          new PerformanceObserver(list => resolve(list.getEntries())).observe(
+            {type: 'paint', buffered: true,
+             includeSoftNavigationObservations: true});
+          });
+        assert_equals(paint_entries.length, 10);
+      },
+      test: "Test that multiple soft navigation buffer paint entries"});
+  </script>
+</body>
+</html>
+
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/navigate-child.html b/testing/web-platform/tests/soft-navigation-heuristics/navigate-child.html
new file mode 100644
index 0000000000..e3c17e2dba
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/navigate-child.html
@@ -0,0 +1,30 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Navigate a child window.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a href="empty.html?2" rel=opener target=child id=link>Click me!</a>
+  </main>
+  <script>
+    promise_test(async t => {
+      const child = window.open("resources/empty.html?1", "child");
+      while (!child.document) {
+        await new Promise(r => t.step_timeout(r, 10));
+      }
+      const link = document.getElementById("link");
+      interact(link);
+      while (!child.location.href.includes("2")) {
+        await new Promise(r => t.step_timeout(r, 10));
+      }
+    }, "Test that a navigated child window doesn't crash");
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-after-transition-commit.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-after-transition-commit.tentative.html
new file mode 100644
index 0000000000..ae17db7d59
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-after-transition-commit.tentative.html
@@ -0,0 +1,28 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect intercepted navigate event with after-transition commit.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a href="foobar.html" id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testNavigationApi("Test soft navigation when navigate event intecepts with { commit: 'after-transition' }", e => {
+        e.intercept({commit: "after-transition", handler: async () => {
+          await addImageToMain();
+          e.commit();
+        }});
+        timestamps[counter]["eventEnd"] = performance.now();
+      }, link);
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-back.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-back.tentative.html
new file mode 100644
index 0000000000..cb96d9caf9
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-back.tentative.html
@@ -0,0 +1,45 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect navigation.back()</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link>Click me!</a>
+    </div>
+  </main>
+  <script>
+    window.onload = async () => {
+      // Wait for after the load event so that the navigation doesn't get converted
+      // into a replace navigation.
+      await new Promise(r => step_timeout(r, 0));
+
+      navigation.onnavigate = e => {
+        e.intercept();
+      };
+      // Push a couple of navigation entries, so that we'd have a navigation entry to go back to.
+      await navigation.navigate("foobar.html").finished;
+      await navigation.navigate("another.html").committed;
+
+      const link = document.getElementById("link");
+      testSoftNavigation({
+        addContent: () => {
+          addTextToDivOnMain();
+        },
+        link: link,
+        pushState: async () =>{
+          await navigation.back().committed;
+        },
+        test: "`navigation.back()` properly works with SoftNavigationHeuristics"});
+    };
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-forward.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-forward.tentative.html
new file mode 100644
index 0000000000..f483ad376b
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-forward.tentative.html
@@ -0,0 +1,48 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect navigation.forward()</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link>Click me!</a>
+    </div>
+  </main>
+  <script>
+    window.onload = async () => {
+      // Wait for after the load event so that the navigation doesn't get converted
+      // into a replace navigation.
+      await new Promise(r => step_timeout(r, 0));
+
+      navigation.onnavigate = e => {
+        e.intercept();
+      };
+      // Push a couple of navigation entries, then go back so that we'd have a
+      // navigation entry to go forward to.
+      await navigation.navigate("other.html").finished;
+      await navigation.navigate("foobar.html").finished;
+      await navigation.back().finished;
+
+      const link = document.getElementById("link");
+      testSoftNavigation({
+        addContent: () => {
+          addTextToDivOnMain();
+        },
+        link: link,
+        pushState: async () =>{
+          await navigation.forward().committed;
+        },
+        test: "`navigation.forward()` properly works with SoftNavigationHeuristics"});
+    };
+  </script>
+</body>
+</html>
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-hash.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-hash.tentative.html
new file mode 100644
index 0000000000..e20578ea79
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-hash.tentative.html
@@ -0,0 +1,28 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect intercepted navigate event.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a href="#foobar.html" id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testNavigationApi("Test soft navigation with the Navigation API", e => {
+        e.intercept({handler: async () => {
+          await addImageToMain();
+          main.appendChild(img);
+        }});
+        timestamps[counter]["eventEnd"] = performance.now();
+      }, link);
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-preventDefault.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-preventDefault.tentative.html
new file mode 100644
index 0000000000..b7b2a24c94
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-preventDefault.tentative.html
@@ -0,0 +1,35 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Don't detect a navigate event which got aborted as a soft navigation.
+</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a href="foobar.html" id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigationNotDetected({
+      testName: "Aborted navigate event is not a soft navigation",
+      eventHandler: e => {
+        e.intercept({handler: async () => {
+          await addImageToMain();
+          main.appendChild(img);
+        }});
+        e.preventDefault();
+        timestamps[counter]["eventEnd"] = performance.now();
+      },
+      eventTarget: navigation,
+      eventName: "navigate",
+      link: link});
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-rejected.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-rejected.tentative.html
new file mode 100644
index 0000000000..693f876b6e
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-rejected.tentative.html
@@ -0,0 +1,28 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect a rejected intercepted navigate event.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a href="foobar.html" id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testNavigationApi("Test intercepted and rejected navigate event", e => {
+        e.intercept({handler: async () => {
+          await addImageToMain();
+          throw new Error("This navigation handler rejected");
+        }});
+        timestamps[counter]["eventEnd"] = performance.now();
+      }, link);
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-traverseto.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-traverseto.tentative.html
new file mode 100644
index 0000000000..e4cabb095a
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-traverseto.tentative.html
@@ -0,0 +1,49 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect navigation.traverseTo()</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link>Click me!</a>
+    </div>
+  </main>
+  <script>
+    let key;
+    window.onload = async () => {
+      // Wait for after the load event so that the navigation doesn't get converted
+      // into a replace navigation.
+      await new Promise(r => step_timeout(r, 0));
+
+      navigation.onnavigate = e => {
+        e.intercept();
+      };
+      // Push a couple of navigation entries, so that we'd have a navigation entry to traverse to.
+      await navigation.navigate("foobar.html").finished;
+      key = navigation.currentEntry.key;
+      await navigation.navigate("another.html").finished;
+
+      const link = document.getElementById("link");
+      testSoftNavigation({
+        addContent: () => {
+          addTextToDivOnMain();
+        },
+        link: link,
+        pushState: async () =>{
+          await navigation.traverseTo(key).committed;
+        },
+        test: "`navigation.traverseTo()` properly works with SoftNavigationHeuristics"});
+    };
+  </script>
+</body>
+</html>
+
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-view-transition.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-view-transition.tentative.html
new file mode 100644
index 0000000000..4d88f3d0b7
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api-view-transition.tentative.html
@@ -0,0 +1,54 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Navigation API + ViewTransition trigger a soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link href="foobar.html">Click me!</a>
+    </div>
+  </main>
+  <script>
+    let key;
+    window.onload = async () => {
+      // Wait for after the load event so that the navigation doesn't get
+      // converted into a replace navigation.
+      await new Promise(r => step_timeout(r, 0));
+
+      const navigate_callback = e => {
+        e.intercept({
+          async handler() {
+            const lcp_promise = new Promise(resolve => {
+             (new PerformanceObserver(list => resolve())).observe(
+               {type: 'largest-contentful-paint',
+                includeSoftNavigationObservations: true});
+             });
+            const transition = document.startViewTransition(async () => {
+              const main = document.getElementById('main');
+              main.innerHTML = '<img id="image" src="/images/blue.png?' +
+                Math.random() + '">';
+              const img = document.getElementById("image");
+            });
+            await transition.updateCallbackDone;
+            await lcp_promise;
+          }
+        });
+        timestamps[counter]["eventEnd"] = performance.now();
+      };
+
+      const link = document.getElementById("link");
+      testNavigationApi("Navigation API interception handler + " +
+                        "startViewTransition properly detects soft navigations",
+                        navigate_callback, link);
+    };
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/navigation-api.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api.tentative.html
new file mode 100644
index 0000000000..2d61736a48
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/navigation-api.tentative.html
@@ -0,0 +1,26 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect intercepted navigate event.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a href="foobar.html" id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testNavigationApi("Test soft navigation with the Navigation API", e => {
+        e.intercept({handler: async () => {
+          await addImageToMain();
+        }});
+        timestamps[counter]["eventEnd"] = performance.now();
+      }, link);
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/popstate-multiple-backs.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/popstate-multiple-backs.tentative.html
new file mode 100644
index 0000000000..fd87f5f03e
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/popstate-multiple-backs.tentative.html
@@ -0,0 +1,64 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Soft navigation with multiple popstate calls.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link>Click me!</a>
+    </div>
+  </main>
+  <script>
+    // Push state 4 times, as history.back() calls will trigger popstate
+   //  events.
+    history.pushState({}, "", "foobar.html");
+    history.pushState({}, "", "another_one.html");
+    history.pushState({}, "", "and_another.html");
+    history.pushState({}, "", "and_yet_another.html");
+
+    // This function runs at the start of the popstate event.
+    const eventPrepWork = t => {
+      // If this is an event due to the first click, go back() twice more.
+      if (!t.popped) {
+        step_timeout(()=>history.back(), 0);
+        step_timeout(()=>history.back(), 0);
+        t.popped = 0;
+      }
+      ++t.popped;
+      // return true for the second time the event fires, which is the first
+      // back() triggered by the popstate event. The means that the first one
+      // of those back() navigations would trigger a soft navigation, but not
+      // the last one.
+      return t.popped == 2;
+    }
+    const link = document.getElementById("link");
+    link.addEventListener("click", () => {
+      history.back();
+      timestamps[counter]["eventEnd"] = performance.now();
+    });
+    testSoftNavigation({
+      addContent: () => {
+        // Add the content to the main element
+        const main = document.getElementById("main");
+        main.removeChild(document.getElementsByTagName("div")[0]);
+        const div = document.createElement("div");
+        const text = document.createTextNode("Lorem ipsum");
+        div.appendChild(text);
+        div.style="font-size: 3em";
+        main.appendChild(div);
+      },
+      link: link,
+      eventPrepWork: eventPrepWork,
+      testName: "A soft navigation that started from a back() call inside a "
+        + "popstate event is recognized by SoftNavigationHeuristics",
+      eventType: "popstate"});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/popstate.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/popstate.tentative.html
new file mode 100644
index 0000000000..f89991d76b
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/popstate.tentative.html
@@ -0,0 +1,50 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link>Click me!</a>
+    </div>
+  </main>
+  <script>
+    // Push state twice, so that history.back() will trigger a popstate event,
+    // when the first push state is restored.
+    history.pushState({}, "", "foobar.html");
+    history.pushState({}, "", "another_one.html");
+
+    const link = document.getElementById("link");
+    link.addEventListener("click", () => {
+      history.back();
+      timestamps[counter]["eventEnd"] = performance.now();
+    });
+    testSoftNavigation({
+      addContent: () => {
+        // Add the content to the main element
+        const main = document.getElementById("main");
+        main.removeChild(document.getElementsByTagName("div")[0]);
+        const div = document.createElement("div");
+        const text = document.createTextNode("Lorem ipsum");
+        div.appendChild(text);
+        div.style="font-size: 3em";
+        main.appendChild(div);
+      },
+      link: link,
+      testName: "A soft navigation that uses a same-document initiated popstate"
+        + " event is recognized by SoftNavigationHeuristics",
+      eventType: "popstate"});
+  </script>
+</body>
+</html>
+
+
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/replacestate-null-then-push.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/replacestate-null-then-push.tentative.html
new file mode 100644
index 0000000000..8a81c6be20
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/replacestate-null-then-push.tentative.html
@@ -0,0 +1,34 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect soft navigation with replaceState that has a null URL, then
+       pushState with the URL.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async (url) => {
+        await addImageToMain();
+        history.pushState({}, '', url);
+      },
+      link: link,
+      pushState: async (url) =>{
+        history.replaceState({}, '');
+      },
+      test: "Detect soft navigation with replaceState that has a null URL," +
+            " then pushState with the URL"});
+  </script>
+</body>
+</html>
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/replacestate.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/replacestate.tentative.html
new file mode 100644
index 0000000000..42e9a71899
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/replacestate.tentative.html
@@ -0,0 +1,28 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect soft navigation with replaceState.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        await addImageToMain();
+      },
+      link: link,
+      pushState: (url)=>{history.replaceState({}, '', url);},
+      test: "Detect soft navigation with replaceState"});
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/resources/empty.html b/testing/web-platform/tests/soft-navigation-heuristics/resources/empty.html
new file mode 100644
index 0000000000..5fa1cdf5e6
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/resources/empty.html
@@ -0,0 +1,2 @@
+<!DOCTYPE HTML>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/resources/history_push.js b/testing/web-platform/tests/soft-navigation-heuristics/resources/history_push.js
new file mode 100644
index 0000000000..6647dd740a
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/resources/history_push.js
@@ -0,0 +1 @@
+history.pushState({}, '', URL);
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/resources/soft-navigation-helper.js b/testing/web-platform/tests/soft-navigation-heuristics/resources/soft-navigation-helper.js
new file mode 100644
index 0000000000..d405adb4e7
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/resources/soft-navigation-helper.js
@@ -0,0 +1,356 @@
+var counter = 0;
+var interacted;
+var timestamps = []
+const MAX_CLICKS = 50;
+// Entries for one hard navigation + 50 soft navigations.
+const MAX_PAINT_ENTRIES = 51;
+const URL = "foobar.html";
+const readValue = (value, defaultValue) => {
+  return value !== undefined ? value : defaultValue;
+}
+const testSoftNavigation =
+    options => {
+      const addContent = options.addContent;
+      const link = options.link;
+      const pushState = readValue(options.pushState,
+        url=>{history.pushState({}, '', url)});
+      const clicks = readValue(options.clicks, 1);
+      const extraValidations = readValue(options.extraValidations,
+                                                   () => {});
+      const testName = options.testName;
+      const pushUrl = readValue(options.pushUrl, true);
+      const eventType = readValue(options.eventType, "click");
+      const interactionFunc = options.interactionFunc;
+      const eventPrepWork = options.eventPrepWork;
+      promise_test(async t => {
+        await waitInitialLCP();
+        const preClickLcp = await getLcpEntries();
+        setEvent(t, link, pushState, addContent, pushUrl, eventType,
+                 eventPrepWork);
+        let first_navigation_id;
+        for (let i = 0; i < clicks; ++i) {
+          const firstClick = (i === 0);
+          let paint_entries_promise =
+              waitOnPaintEntriesPromise(firstClick);
+          interacted = false;
+          interact(link, interactionFunc);
+
+          const navigation_id = await waitOnSoftNav();
+          if (!first_navigation_id) {
+            first_navigation_id = navigation_id;
+          }
+          // Ensure paint timing entries are fired before moving on to the next
+          // click.
+          await paint_entries_promise;
+        }
+        assert_equals(
+            document.softNavigations, clicks,
+            'Soft Navigations detected are the same as the number of clicks');
+        await validateSoftNavigationEntry(
+            clicks, extraValidations, pushUrl);
+
+        await runEntryValidations(preClickLcp, first_navigation_id, clicks + 1, options.validate);
+      }, testName);
+    };
+
+const testNavigationApi = (testName, navigateEventHandler, link) => {
+  promise_test(async t => {
+    navigation.addEventListener('navigate', navigateEventHandler);
+    const navigated = new Promise(resolve => {
+      navigation.addEventListener('navigatesuccess', resolve);
+      navigation.addEventListener('navigateerror', resolve);
+    });
+    await waitInitialLCP();
+    const preClickLcp = await getLcpEntries();
+    let paint_entries_promise = waitOnPaintEntriesPromise();
+    interact(link);
+    const first_navigation_id = await waitOnSoftNav();
+    await navigated;
+    await paint_entries_promise;
+    assert_equals(document.softNavigations, 1, 'Soft Navigation detected');
+    await validateSoftNavigationEntry(1, () => {}, 'foobar.html');
+
+    await runEntryValidations(preClickLcp, first_navigation_id);
+  }, testName);
+};
+
+const testSoftNavigationNotDetected = options => {
+    promise_test(async t => {
+      const preClickLcp = await getLcpEntries();
+      options.eventTarget.addEventListener(options.eventName, options.eventHandler);
+      interact(options.link);
+      await new Promise((resolve, reject) => {
+        (new PerformanceObserver(() =>
+            reject("Soft navigation should not be triggered"))).observe({
+          type: 'soft-navigation',
+          buffered: true
+        });
+        t.step_timeout(resolve, 1000);
+      });
+      if (document.softNavigations) {
+        assert_equals(
+          document.softNavigations, 0, 'Soft Navigation not detected');
+      }
+      const postClickLcp = await getLcpEntries();
+      assert_equals(
+          preClickLcp.length, postClickLcp.length, 'No LCP entries accumulated');
+    }, options.testName);
+  };
+
+const runEntryValidations =
+    async (preClickLcp, first_navigation_id, entries_expected_number = 2,
+           validate = null) => {
+  await validatePaintEntries('first-contentful-paint', entries_expected_number,
+                             first_navigation_id);
+  await validatePaintEntries('first-paint', entries_expected_number,
+                             first_navigation_id);
+  const postClickLcp = await getLcpEntries();
+  const postClickLcpWithoutSoftNavs = await getLcpEntriesWithoutSoftNavs();
+  assert_greater_than(
+      postClickLcp.length, preClickLcp.length,
+      'Soft navigation should have triggered at least an LCP entry');
+
+  if (validate) {
+    await validate();
+  }
+  assert_equals(
+      postClickLcpWithoutSoftNavs.length, preClickLcp.length,
+      'Soft navigation should not have triggered an LCP entry when the ' +
+      'observer did not opt in');
+  assert_not_equals(
+      postClickLcp[postClickLcp.length - 1].size,
+      preClickLcp[preClickLcp.length - 1].size,
+      'Soft navigation LCP element should not have identical size to the hard ' +
+          'navigation LCP element');
+  assert_equals(
+      postClickLcp[preClickLcp.length].navigationId,
+      first_navigation_id, 'Soft navigation LCP should have the same navigation ' +
+      'ID as the last soft nav entry')
+};
+
+const interact =
+    (link, interactionFunc = undefined) => {
+      if (test_driver) {
+        if (interactionFunc) {
+          interactionFunc();
+        } else {
+          test_driver.click(link);
+        }
+        timestamps[counter] = {"syncPostInteraction": performance.now()};
+      }
+    }
+
+const setEvent = (t, button, pushState, addContent, pushUrl, eventType, prepWork) => {
+  const eventObject =
+      (eventType == 'click' || eventType.startsWith("key")) ? button : window;
+  eventObject.addEventListener(eventType, async e => {
+    let prepWorkFailed = false;
+    if (prepWork &&!prepWork(t)) {
+      prepWorkFailed = true;
+    }
+    // This is the end of the event's sync processing.
+    if (!timestamps[counter]["eventEnd"]) {
+      timestamps[counter]["eventEnd"] = performance.now();
+    }
+    if (prepWorkFailed) {
+      return;
+    }
+    // Jump through a task, to ensure task tracking is working properly.
+    await new Promise(r => t.step_timeout(r, 0));
+
+    const url = URL + "?" + counter;
+    if (pushState) {
+      // Change the URL
+      if (pushUrl) {
+        pushState(url);
+      } else {
+        pushState();
+      }
+    }
+
+    // Wait 10 ms to make sure the timestamps are correct.
+    await new Promise(r => t.step_timeout(r, 10));
+
+    await addContent(url);
+
+    interacted = true;
+    ++counter;
+  });
+};
+
+const validateSoftNavigationEntry = async (clicks, extraValidations,
+                                              pushUrl) => {
+  const [entries, options] = await new Promise(resolve => {
+    (new PerformanceObserver((list, obs, options) => resolve(
+      [list.getEntries(), options]))).observe(
+      {type: 'soft-navigation', buffered: true});
+    });
+  const expectedClicks = Math.min(clicks, MAX_CLICKS);
+
+  assert_equals(entries.length, expectedClicks,
+                "Performance observer got an entry");
+  for (let i = 0; i < entries.length; ++i) {
+    const entry = entries[i];
+    assert_true(entry.name.includes(pushUrl ? URL : document.location.href),
+                "The soft navigation name is properly set");
+    const entryTimestamp = entry.startTime;
+    assert_less_than_equal(timestamps[i]["syncPostInteraction"], entryTimestamp,
+                "Entry timestamp is lower than the post interaction one");
+    assert_greater_than_equal(
+        entryTimestamp, timestamps[i]['eventEnd'],
+        'Event start timestamp matches');
+    assert_not_equals(entry.navigationId,
+                      performance.getEntriesByType("navigation")[0].navigationId,
+      "The navigation ID was re-generated and different from the initial one.");
+    if (i > 0) {
+      assert_not_equals(entry.navigationId,
+                        entries[i-1].navigationId,
+        "The navigation ID was re-generated between clicks");
+    }
+  }
+  assert_equals(performance.getEntriesByType("soft-navigation").length,
+                expectedClicks, "Performance timeline got an entry");
+  await extraValidations(entries, options);
+
+};
+
+const validatePaintEntries = async (type, entries_number, first_navigation_id) => {
+  if (!performance.softNavPaintMetricsSupported) {
+    return;
+  }
+  const expected_entries_number = Math.min(entries_number, MAX_PAINT_ENTRIES);
+  const entries = await new Promise(resolve => {
+    const entries = [];
+    (new PerformanceObserver(list => {
+      entries.push(...list.getEntriesByName(type));
+      if (entries.length >= expected_entries_number) {
+        resolve(entries);
+      }
+    })).observe(
+      {type: 'paint', buffered: true, includeSoftNavigationObservations: true});
+    });
+  const entries_without_softnavs = await new Promise(resolve => {
+    (new PerformanceObserver(list => resolve(
+      list.getEntriesByName(type)))).observe(
+      {type: 'paint', buffered: true});
+    });
+  assert_equals(entries.length, expected_entries_number,
+    `There are ${entries_number} entries for ${type}`);
+  assert_equals(entries_without_softnavs.length, 1,
+    `There is one non-softnav entry for ${type}`);
+  if (entries_number > 1) {
+    assert_not_equals(entries[0].startTime, entries[1].startTime,
+      "Entries have different timestamps for " + type);
+  }
+  if (expected_entries_number > entries_without_softnavs.length) {
+    assert_equals(entries[entries_without_softnavs.length].navigationId,
+      first_navigation_id,
+      "First paint entry should have the same navigation ID as the last soft " +
+      "navigation entry");
+  }
+};
+
+const waitInitialLCP = () => {
+  return new Promise(resolve => {
+      new PerformanceObserver(list => resolve()).observe({
+        type: 'largest-contentful-paint',
+        buffered: true
+      });
+  });
+}
+
+const waitOnSoftNav = () => {
+  return new Promise(resolve => {
+    (new PerformanceObserver(list => {
+       const entries = list.getEntries();
+       assert_equals(entries.length, 1,
+                     "Only one soft navigation entry");
+       resolve(entries[0].navigationId);
+    })).observe({
+      type: 'soft-navigation'
+    });
+  });
+};
+
+const getLcpEntries = async () => {
+  const entries = await new Promise(resolve => {
+    (new PerformanceObserver(list => resolve(
+      list.getEntries()))).observe(
+      {type: 'largest-contentful-paint', buffered: true,
+       includeSoftNavigationObservations: true});
+    });
+  return entries;
+};
+
+const getLcpEntriesWithoutSoftNavs = async () => {
+  const entries = await new Promise(resolve => {
+    (new PerformanceObserver(list => resolve(
+      list.getEntries()))).observe(
+      {type: 'largest-contentful-paint', buffered: true});
+    });
+  return entries;
+};
+
+const addImage = async (element, url="blue.png", id = "imagelcp") => {
+  const img = new Image();
+  img.src = '/images/'+ url + "?" + Math.random();
+  img.id=id
+  img.setAttribute("elementtiming", id);
+  await img.decode();
+  element.appendChild(img);
+};
+const addImageToMain = async (url="blue.png", id = "imagelcp") => {
+  await addImage(document.getElementById('main'), url, id);
+};
+
+const addTextParagraphToMain = (text, element_timing = "") => {
+  const main = document.getElementById("main");
+  const p = document.createElement("p");
+  const textNode = document.createTextNode(text);
+  p.appendChild(textNode);
+  if (element_timing) {
+    p.setAttribute("elementtiming", element_timing);
+  }
+  p.style = "font-size: 3em";
+  main.appendChild(p);
+  return p;
+};
+const addTextToDivOnMain = () => {
+  const main = document.getElementById("main");
+  const prevDiv = document.getElementsByTagName("div")[0];
+  if (prevDiv) {
+    main.removeChild(prevDiv);
+  }
+  const div = document.createElement("div");
+  const text = document.createTextNode("Lorem Ipsum");
+  div.appendChild(text);
+  div.style = "font-size: 3em";
+  main.appendChild(div);
+}
+
+const waitOnPaintEntriesPromise = (expectLCP = true) => {
+  return new Promise((resolve, reject) => {
+    if (performance.softNavPaintMetricsSupported) {
+      const paint_entries = []
+      new PerformanceObserver(list => {
+        paint_entries.push(...list.getEntries());
+        if (paint_entries.length == 2) {
+          resolve();
+        } else if (paint_entries.length > 2) {
+          reject();
+        }
+      }).observe({type: 'paint', includeSoftNavigationObservations: true});
+    } else if (expectLCP) {
+        new PerformanceObserver(list => {
+          resolve();
+        }).observe({
+          type: 'largest-contentful-paint',
+          includeSoftNavigationObservations: true
+        });
+    } else {
+        step_timeout(
+            () => requestAnimationFrame(() => requestAnimationFrame(resolve)),
+            100);
+    }
+  });
+};
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/second-interaction-not-softnav.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/second-interaction-not-softnav.tentative.html
new file mode 100644
index 0000000000..a9bb337060
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/second-interaction-not-softnav.tentative.html
@@ -0,0 +1,35 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <p><a id=link>Click me!</a></p>
+  <p><a id=secondlink>Then click me!</a></p>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        if (test_driver) {
+          const secondlink = document.getElementById("secondlink");
+          const clickPromise = new Promise(r => {
+            secondlink.addEventListener("click", r);
+          });
+          test_driver.click(secondlink);
+          await clickPromise;
+        }
+        addImageToMain();
+      },
+      link: link,
+      test: "Second interaction in the middle of a soft navigation"});
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-main-descendent.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-main-descendent.tentative.html
new file mode 100644
index 0000000000..96ff55260c
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-main-descendent.tentative.html
@@ -0,0 +1,30 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect soft navigation adding content to a main descendent.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  <div id=descendent></div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: () => {
+        const descendent= document.getElementById("descendent");
+        const content = document.createTextNode("Lorem Ipsum");
+        descendent.appendChild(content);
+      },
+      link: link,
+      test: "Test that a soft navigation is detected even when DOM change is "
+        + "done on a main descendent"});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-non-main.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-non-main.tentative.html
new file mode 100644
index 0000000000..86da167c33
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-non-main.tentative.html
@@ -0,0 +1,25 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <a id=link>Click me!</a>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        await addImage(document.body);
+      },
+      link: link,
+      test: "Test that a soft navigation is detected on a non-main element"});
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-web-component-lifecycle.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-web-component-lifecycle.tentative.html
new file mode 100644
index 0000000000..7e27b0073c
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection-web-component-lifecycle.tentative.html
@@ -0,0 +1,46 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <script>
+    // Define a custom element
+    class SPAContent extends HTMLDivElement {
+      constructor() {
+        super();
+      }
+      connectedCallback() {
+        // Change the URL
+        history.pushState({}, '', "/foobar.html");
+      }
+    }
+    customElements.define("spa-content", SPAContent, { extends: "div"});
+
+  </script>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: () => {
+        const main = document.getElementById("main");
+        const spaContent = document.createElement("div", {is: "spa-content"});
+        const content = document.createTextNode("Lorem Ipsum");
+        spaContent.appendChild(content);
+        main.appendChild(spaContent);
+      },
+      link: link,
+      test: "Test that a soft navigation is detected when the click is done  "
+        + "on a custom element."});
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection.tentative.html
new file mode 100644
index 0000000000..618984d859
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-detection.tentative.html
@@ -0,0 +1,26 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        await addImageToMain();
+      },
+      link: link,
+      test: "Test that a soft navigation is detected"});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-no-url.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-no-url.tentative.html
new file mode 100644
index 0000000000..a0055c654c
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/soft-navigation-no-url.tentative.html
@@ -0,0 +1,31 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigationNotDetected({
+      eventHandler: url => {
+        addTextToDivOnMain();
+        history.pushState({}, '');
+      },
+      link: link,
+      eventName: "click",
+      eventTarget: link,
+      testName: "Test that a soft navigation is not detected when a URL is not"
+        + " passed to the history API."});
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/softnav-after-lcp-paint-larger-than-viewport.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/softnav-after-lcp-paint-larger-than-viewport.tentative.html
new file mode 100644
index 0000000000..3c930d8be4
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/softnav-after-lcp-paint-larger-than-viewport.tentative.html
@@ -0,0 +1,70 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="/soft-navigation-heuristics/resources/soft-navigation-helper.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img id="initial_image1" src="/images/lcp-256x256.png?1" style="width: 90vw; height: 90vh">
+        <div id=extra></div>
+      </a>
+    </div>
+  </main>
+  <script>
+  (async () => {
+    const link = document.getElementById("link");
+
+    // Inject a second image that takes a large part of the viewport.
+    await new Promise(resolve => {
+      requestAnimationFrame(() => requestAnimationFrame(() => {
+        document.getElementById("extra").innerHTML = `
+          <div style="position: absolute; bottom: 0; right: 0">
+            <img id="initial_image2" src="/images/lcp-256x256.png?2" style="width: 90vw;height: 90vh">
+          </div>`;
+        resolve();
+      }));
+    });
+    // Wait until the second image is rendered.
+    await new Promise(resolve => {
+      requestAnimationFrame(() => requestAnimationFrame(() => {
+        resolve();
+      }));
+    });
+    testSoftNavigation({
+      addContent: async () => {
+        // Remove the initial image, so that the text would be painted on screen.
+        document.getElementById("initial_image1").remove();
+        document.getElementById("initial_image2").remove();
+        let lcp_element_painted;
+        const lcp_element_paint_promise = new Promise((r) => { lcp_element_painted = r; });
+        // Add an LCP element, but have it be small enough to not trigger the
+        // Soft Navigation heuristics.
+        const p = addTextParagraphToMain(
+          "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod",
+          /*element_timing=*/"lcp");
+        (new PerformanceObserver(list => {
+          // Once the first element is fully painted:
+          lcp_element_painted();
+        })).observe({type: "element", buffered: true});
+        await lcp_element_paint_promise;
+        // Add a smaller element that gets us over that threshold.
+        addTextParagraphToMain("dolore magna aliqua.");
+      },
+      link: link,
+      test: "Test that an image LCP followed by a smaller soft navigation LCP"
+        + " properly queues an LCP entry, even when the soft navigation is"
+        + " detected after the LCP, even when initial paints significantly"
+        + " exceed the viewport dimensions."});
+  })();
+  </script>
+</body>
+</html>
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/softnav-after-lcp-paint.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/softnav-after-lcp-paint.tentative.html
new file mode 100644
index 0000000000..cf9a9942ca
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/softnav-after-lcp-paint.tentative.html
@@ -0,0 +1,42 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img src="/images/lcp-256x256.png"></a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        let lcp_element_painted;
+        const lcp_element_paint_promise = new Promise((r) => { lcp_element_painted = r; });
+        // Add an LCP element, but have it be small enough to not trigger the
+        // Soft Navigation heuristics.
+        const p = addTextParagraphToMain("Lorem Ipsu", /*element_timing=*/"lcp");
+        (new PerformanceObserver(list => {
+          // Once the first element is fully painted:
+          lcp_element_painted();
+        })).observe({type: "element", buffered: true});
+        await lcp_element_paint_promise;
+        // Add a smaller element that gets us over that threshold.
+        addTextParagraphToMain("m");
+      },
+      link: link,
+      test: "Test that an image LCP followed by a smaller soft navigation LCP"
+        + " properly queues an LCP entry, even when the soft navigation is"
+        + " detected after the LCP."});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/softnav-before-lcp-paint.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/softnav-before-lcp-paint.tentative.html
new file mode 100644
index 0000000000..d5dc4b74fb
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/softnav-before-lcp-paint.tentative.html
@@ -0,0 +1,52 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img src="/images/lcp-256x256.png"></a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        // Add an LCP element, large enough to trigger the Soft Navigation
+        // heuristics.
+        const p = addTextParagraphToMain("Lorem Ipsum", /*element_timing=*/"lcp");
+        p.id = "first_lcp";
+        // Once the first element is fully painted.
+        const observer = new PerformanceObserver(list => {
+          // Add a larger element to be the new LCP.
+          window.lcp_observer_promise = new Promise(resolve => {
+            (new PerformanceObserver(resolve)).observe({type: "element"});
+          });
+          const p2 = addTextParagraphToMain("LOREM IPSUMER", "real_lcp");
+          p2.id = "real_lcp";
+          observer.disconnect();
+        });
+        observer.observe({type: "element", buffered: true});
+      },
+      link: link,
+      validate: async () => {
+        await window.lcp_observer_promise;
+        const lcps = await getLcpEntries();
+        assert_greater_than_equal(lcps.length, 3, "Got at least 3 LCP entries");
+        assert_equals(lcps[lcps.length - 2].id, "first_lcp", "Got the first LCP");
+        assert_equals(lcps[lcps.length - 1].id, "real_lcp", "Got the real LCP");
+      },
+      test: "Test that an image LCP followed by 2 smaller soft navigation LCPs"
+        + " properly queues both LCP entries, even when the soft navigation"
+        + " is detected in between them."});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/softnav-between-lcp-render-and-paint.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/softnav-between-lcp-render-and-paint.tentative.html
new file mode 100644
index 0000000000..56c7073de6
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/softnav-between-lcp-render-and-paint.tentative.html
@@ -0,0 +1,36 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img src="/images/lcp-256x256.png"></a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        // Add an LCP element, but have it be small enough to not trigger the
+        // Soft Navigation heuristics.
+        const p = addTextParagraphToMain("Lorem Ipsu");
+        requestAnimationFrame(() => {
+          const p2 = addTextParagraphToMain("m");
+        });
+      },
+      link: link,
+      test: "Test that an image LCP followed by a smaller soft navigation LCP"
+        + " properly queues an LCP entry, even when the soft navigation is"
+        + " detected between the LCP's render and paint."});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/supported-entry-types.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/supported-entry-types.tentative.html
new file mode 100644
index 0000000000..4ab408e10b
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/supported-entry-types.tentative.html
@@ -0,0 +1,15 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Soft navigations are a supported entry type</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+  promise_test(async () => {
+    assert_true(PerformanceObserver.supportedEntryTypes.includes(
+      "soft-navigation"));
+  }, "Soft navigations are a supported entry type");
+</script>
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-before-detection-second-softnav.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-before-detection-second-softnav.tentative.html
new file mode 100644
index 0000000000..bed27c3506
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-before-detection-second-softnav.tentative.html
@@ -0,0 +1,62 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img src="/images/lcp-256x256.png" id="img"></a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    let first_lcp_painted;
+    let second_lcp_painted;
+    (async () => {
+      await new Promise(r => { first_lcp_painted = r; });
+      addTextParagraphToMain("LOREM IPSUMR", "no lcp");
+      (new PerformanceObserver(second_lcp_painted)).observe({type: "element"});
+    })();
+    testSoftNavigation({
+      pushState: null,
+      clicks: 2,
+      addContent: async () => {
+        // Add an LCP element.
+        await new Promise(resolve => {
+          const p = addTextParagraphToMain("Lorem Ipsum", /*element_timing=*/"first_lcp" + counter);
+          p.id = "first_lcp" + counter;
+          (new PerformanceObserver(resolve)).observe({type: "element"});
+        });
+        if(counter) {
+          first_lcp_painted();
+          // Wait for the unrelated LCP to be painted.
+          await new Promise(r => { second_lcp_painted = r; });
+        }
+        const url = URL + "?" + counter;
+        history.pushState({}, '', url);
+      },
+      link: link,
+      validate: async () => {
+        const lcps = await getLcpEntries();
+        const ref_counter = counter-1;
+        assert_equals(lcps.length, 2 + ref_counter, "Got 2 LCP entries");
+        assert_equals(lcps[lcps.length - 1].id, "first_lcp" + ref_counter, "Got the first LCP");
+      },
+      test: "Second soft navigation text LCP discovered between user " +
+            "interaction and soft navigation detection are properly " +
+            "reported, while unrelated LCPs are ignored during that time. " +
+            "As a side effect, we also test element timing."});
+  </script>
+</body>
+</html>
+
+
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-before-detection.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-before-detection.tentative.html
new file mode 100644
index 0000000000..11e82e539f
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-before-detection.tentative.html
@@ -0,0 +1,55 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link><img src="/images/lcp-256x256.png" id="img"></a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    let first_lcp_painted;
+    let second_lcp_painted;
+    (async () => {
+      await new Promise(r => { first_lcp_painted = r; });
+      addTextParagraphToMain("LOREM IPSUMR", "no lcp");
+      (new PerformanceObserver(second_lcp_painted)).observe({type: "element"});
+    })();
+    testSoftNavigation({
+      pushState: null,
+      addContent: async () => {
+        // Add an LCP element.
+        await new Promise(resolve => {
+          const p = addTextParagraphToMain("Lorem Ipsum", /*element_timing=*/"first_lcp");
+          p.id = "first_lcp";
+          (new PerformanceObserver(resolve)).observe({type: "element"});
+        });
+        first_lcp_painted();
+        // Wait for the unrelated LCP to be painted.
+        await new Promise(r => { second_lcp_painted = r; });
+        const url = URL + "?" + counter;
+        history.pushState({}, '', url);
+      },
+      link: link,
+      validate: async () => {
+        const lcps = await getLcpEntries();
+        assert_equals(lcps.length, 2, "Got 2 LCP entries");
+        assert_equals(lcps[lcps.length - 1].id, "first_lcp", "Got the first LCP");
+      },
+      test: "Text LCP discovered between user interaction and soft " +
+            "navigation detection are properly reported, while unrelated " +
+            "LCPs are ignored during that time. As a side effect, we also " +
+            "test element timing."});
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-anim-image-softnav-lcp.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-anim-image-softnav-lcp.tentative.html
new file mode 100644
index 0000000000..0615b513e6
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-anim-image-softnav-lcp.tentative.html
@@ -0,0 +1,32 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link style="font-size: 4em">Click me!</a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        const main = document.getElementById("main");
+        main.removeChild(document.getElementsByTagName("div")[0]);
+        await addImageToMain("anim-gr.png");
+      },
+      link: link,
+      test: "Test that a text LCP followup by a smaller soft navigation image"
+        + " LCP properly queues an LCP entry"});
+  </script>
+</body>
+</html>
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-image-softnav-lcp.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-image-softnav-lcp.tentative.html
new file mode 100644
index 0000000000..3a8398347c
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-image-softnav-lcp.tentative.html
@@ -0,0 +1,31 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link style="font-size: 4em">Click me!</a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        const main = document.getElementById("main");
+        main.removeChild(document.getElementsByTagName("div")[0]);
+        await addImageToMain();
+      },
+      link: link,
+      test: "Test that a text LCP followup by a smaller soft navigation image"
+        + " LCP properly queues an LCP entry"});
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-text-softnav-lcp.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-text-softnav-lcp.tentative.html
new file mode 100644
index 0000000000..929f59f019
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/text-lcp-followed-by-text-softnav-lcp.tentative.html
@@ -0,0 +1,34 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Detect simple soft navigation.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+    <div>
+      <a id=link style="font-size: 4em">Click me!</a>
+    </div>
+  </main>
+  <script>
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: () => {
+        const main = document.getElementById("main");
+        main.removeChild(document.getElementsByTagName("div")[0]);
+        addTextToDivOnMain();
+      },
+      link: link,
+      test: "Test that a text LCP followup by a smaller soft navigation text"
+        + " LCP properly queues an LCP entry"});
+  </script>
+</body>
+</html>
+
+
+
diff --git a/testing/web-platform/tests/soft-navigation-heuristics/visited-link.tentative.html b/testing/web-platform/tests/soft-navigation-heuristics/visited-link.tentative.html
new file mode 100644
index 0000000000..0bb149f00e
--- /dev/null
+++ b/testing/web-platform/tests/soft-navigation-heuristics/visited-link.tentative.html
@@ -0,0 +1,48 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Soft navigation visited link paint tests.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/soft-navigation-helper.js"></script>
+</head>
+<body>
+  <main id=main>
+  <a id=link>Click me!</a>
+  <a id=visited>link that is really long so it is the LCP</a>
+  </main>
+  <script>
+    const visited = document.getElementById("visited");
+    const fake_url = "./fake_" + Math.random();
+    visited.href = fake_url;
+    const visitFakeURLAndAddInvisibleText = () => {
+      requestAnimationFrame(() => requestAnimationFrame(() => {
+        history.replaceState({}, "", fake_url);
+      }));
+      const main = document.getElementById("main");
+      const div = document.createElement("div");
+      const text = document.createTextNode("Lorem Ipsum");
+      div.appendChild(text);
+      main.appendChild(div);
+    }
+    const link = document.getElementById("link");
+    testSoftNavigation({
+      addContent: async () => {
+        await visitFakeURLAndAddInvisibleText();
+      },
+      link: link,
+      validate: async () => {
+        await new Promise(r => step_timeout(r, 100));
+        const postVisitedLcp = await getLcpEntries();
+        assert_not_equals(postVisitedLcp[postVisitedLcp.length - 1].id,
+                          "visited",
+                          "Soft Nav LCP ID should not be visited");
+      },
+      test: "Test that a visited link doesn't trigger LCP after a soft " +
+            "navigation is detected"});
+  </script>
+</body>
+</html>
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