1 files changed, 108 insertions, 0 deletions
diff --git a/gfx/layers/apz/test/mochitest/helper_scroll_linked_effect_detector.html b/gfx/layers/apz/test/mochitest/helper_scroll_linked_effect_detector.html
new file mode 100644
index 0000000000..aaa4b43829
--- /dev/null
+++ b/gfx/layers/apz/test/mochitest/helper_scroll_linked_effect_detector.html
@@ -0,0 +1,108 @@
+<!DOCTYPE html>
+<html>
+<meta charset="utf-8">
+<script src="/tests/SimpleTest/paint_listener.js"></script>
+<script src="apz_test_utils.js"></script>
+<script src="apz_test_native_event_utils.js"></script>
+<title>ScrollLinkedEffectDetector tests</title>
+<style>
+html, body { margin: 0; }
+body {
+  height: 1000vh;
+}
+#target {
+  position: absolute;
+  height: 800px;
+  background-color: #cc00cc;
+  top: 0;
+  left: 0;
+  right: 0;
+}
+</style>
+<div id="target"></div>
+<script>
+async function test() {
+  let eventTimeStamp;
+  // Utility function to synthesize a scroll and call the given function
+  // in the event listener.
+  async function promiseScrollAndEvent(fn) {
+    let scrollEventPromise = new Promise(resolve => {
+      window.addEventListener("scroll", () => {
+        fn();
+        resolve();
+      }, { once: true });
+    });
+    await scrollEventPromise;
+    // Wait a rAF to make sure we are outside of the micro tasks for the scroll
+    // event callback so that we can ensure our stack based
+    // ScrollLinkedEffectDetector has been scoped out from the function firing
+    // scroll events.
+    await promiseFrame();
+  }
+
+  let intervalId = setInterval(async () => {
+    await synthesizeNativeWheel(window, 50, 50, 0, -10);
+  }, 0);
+  await promiseScrollAndEvent(() => {
+    eventTimeStamp = document.timeline.currentTime;
+  });
+  is(eventTimeStamp, document.timeline.currentTime,
+     `We are in same time frame where we got a scroll event at ${eventTimeStamp}`);
+  ok(!SpecialPowers.DOMWindowUtils.hasScrollLinkedEffect,
+     "No scroll-linked effect found yet");
+
+  // Setup a scroll-linked effect callback.
+  await promiseScrollAndEvent(() => {
+    isnot(window.scrollY, 0, "we've already scrolled some amount");
+    target.style.top = window.scrollY + "px";
+    eventTimeStamp = document.timeline.currentTime;
+  });
+  is(eventTimeStamp, document.timeline.currentTime,
+     `We are in same time frame where we got a scroll event at ${eventTimeStamp}`);
+  ok(SpecialPowers.DOMWindowUtils.hasScrollLinkedEffect,
+     "Scroll-linked effect found");
+
+  // A no-op again.
+  await promiseScrollAndEvent(() => {
+    eventTimeStamp = document.timeline.currentTime;
+  });
+  is(eventTimeStamp, document.timeline.currentTime,
+     `We are in same time frame where we got a scroll event at ${eventTimeStamp}`);
+  ok(!SpecialPowers.DOMWindowUtils.hasScrollLinkedEffect,
+     "No scroll-linked effect found");
+
+  // Setup a non-effective scroll-linked effect callback.
+  await promiseScrollAndEvent(() => {
+    target.style.top = getComputedStyle(target).top;
+    eventTimeStamp = document.timeline.currentTime;
+  });
+  is(eventTimeStamp, document.timeline.currentTime,
+     `We are in same time frame where we got a scroll event at ${eventTimeStamp}`);
+  ok(!SpecialPowers.DOMWindowUtils.hasScrollLinkedEffect,
+     "No scroll-linked effect found");
+
+  // Setup a callback to remove the style.
+  await promiseScrollAndEvent(() => {
+    target.style.top = "";
+    eventTimeStamp = document.timeline.currentTime;
+  });
+  is(eventTimeStamp, document.timeline.currentTime,
+     `We are in same time frame where we got a scroll event at ${eventTimeStamp}`);
+  ok(SpecialPowers.DOMWindowUtils.hasScrollLinkedEffect,
+     "Scroll-linked effect found");
+
+  // Setup a no-op callback.
+  await promiseScrollAndEvent(() => {
+    eventTimeStamp = document.timeline.currentTime;
+  });
+  is(eventTimeStamp, document.timeline.currentTime,
+     `We are in same time frame where we got a scroll event at ${eventTimeStamp}`);
+  ok(!SpecialPowers.DOMWindowUtils.hasScrollLinkedEffect,
+     "No scroll-linked effect found this time");
+  clearInterval(intervalId);
+}
+
+waitUntilApzStable()
+.then(test)
+.then(subtestDone, subtestFailed);
+</script>