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diff --git a/testing/web-platform/tests/scroll-to-text-fragment/same-document-tests.html b/testing/web-platform/tests/scroll-to-text-fragment/same-document-tests.html
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index 0000000000..be9bed9fd8
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+++ b/testing/web-platform/tests/scroll-to-text-fragment/same-document-tests.html
@@ -0,0 +1,80 @@
+<!doctype html>
+<title>Same document navigation to text fragment directives</title>
+<meta charset=utf-8>
+<link rel="help" href="https://wicg.github.io/ScrollToTextFragment/">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+  function reset() {
+    location.hash = '';
+    window.scrollTo(0, 0);
+  }
+
+  function isInViewport(element) {
+    const viewportRect = {
+      left: visualViewport.offsetLeft,
+      top: visualViewport.offsetTop,
+      right: visualViewport.offsetLeft + visualViewport.width,
+      bottom: visualViewport.offsetTop + visualViewport.height
+    };
+
+    const elementRect = element.getBoundingClientRect();
+    const elementCenter = {
+      x: elementRect.left + elementRect.width / 2,
+      y: elementRect.top + elementRect.height / 2
+    };
+
+    return elementCenter.x > viewportRect.left &&
+           elementCenter.x < viewportRect.right &&
+           elementCenter.y > viewportRect.top &&
+           elementCenter.y < viewportRect.bottom;
+  }
+
+  function runTests() {
+    // Ensure a simple text directive works correctly when navigated to the
+    // same document using `location.hash`.
+    promise_test(async t => {
+      assert_implements(document.fragmentDirective, 'Text directive not implemented');
+      reset();
+
+      location.hash = ':~:text=line%20of%20text';
+      await t.step_wait(() => window.scrollY > 0, "Wait for scroll");
+      assert_true(isInViewport(document.getElementById('text')), 'Scrolled to text');
+    }, 'Basic text directive navigation');
+
+    // Test that we correctly fallback to the element id when we have a text
+    // directive that doesn't match any text in the page.
+    promise_test(async t => {
+      assert_implements(document.fragmentDirective, 'Text directive not implemented');
+      reset();
+
+      location.hash = 'elementid:~:text=textDoesntExist';
+      await t.step_wait(() => window.scrollY > 0, "Wait for scroll");
+      assert_true(isInViewport(document.getElementById('elementid')), 'Scrolled to `elementid`');
+    }, 'Basic element id fallback');
+
+    // Test that we correctly fallback to the element id when we have a text
+    // directive that's malformed and won't be parsed.
+    promise_test(async t => {
+      assert_implements(document.fragmentDirective, 'Text directive not implemented');
+      reset();
+
+      location.hash = 'elementid:~:text=,,,,,';
+      await t.step_wait(() => window.scrollY > 0, "Wait for scroll");
+      assert_true(isInViewport(document.getElementById('elementid')), 'Scrolled to `elementid`');
+    }, 'Malformed text directive element id fallback');
+  }
+</script>
+<style>
+  div {
+    margin: 200vh 0 200vh 0;
+  }
+</style>
+<body onload="runTests()">
+  <div id="text">
+    This is a line of text.
+  </div>
+  <div id="elementid">
+    This div has an id: 'elementid'.
+  </div>
+</body>