1 files changed, 105 insertions, 0 deletions
diff --git a/gfx/layers/apz/test/mochitest/browser_test_position_sticky.js b/gfx/layers/apz/test/mochitest/browser_test_position_sticky.js
new file mode 100644
index 0000000000..ce6b093a80
--- /dev/null
+++ b/gfx/layers/apz/test/mochitest/browser_test_position_sticky.js
@@ -0,0 +1,105 @@
+/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set sts=2 sw=2 et tw=80: */
+"use strict";
+
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/gfx/layers/apz/test/mochitest/apz_test_utils.js",
+  this
+);
+
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/gfx/layers/apz/test/mochitest/apz_test_native_event_utils.js",
+  this
+);
+
+add_task(async () => {
+  function httpURL(filename) {
+    let chromeURL = getRootDirectory(gTestPath) + filename;
+    return chromeURL.replace(
+      "chrome://mochitests/content/",
+      "http://mochi.test:8888/"
+    );
+  }
+
+  const url = httpURL("helper_position_sticky_flicker.html");
+  const tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, url);
+
+  const { rect, scrollbarWidth } = await SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [],
+    async () => {
+      const sticky = content.document.getElementById("sticky");
+
+      // Get the area in the screen coords where the position:sticky element is.
+      let stickyRect = sticky.getBoundingClientRect();
+      stickyRect.x += content.window.mozInnerScreenX;
+      stickyRect.y += content.window.mozInnerScreenY;
+
+      // generate some DIVs to make the page complex enough.
+      for (let i = 1; i <= 120000; i++) {
+        const div = content.document.createElement("div");
+        div.innerText = `${i}`;
+        content.document.body.appendChild(div);
+      }
+
+      await content.wrappedJSObject.promiseApzFlushedRepaints();
+      await content.wrappedJSObject.waitUntilApzStable();
+
+      let w = {},
+        h = {};
+      SpecialPowers.DOMWindowUtils.getScrollbarSizes(
+        content.document.documentElement,
+        w,
+        h
+      );
+
+      // Reduce the scrollbar width from the sticky area.
+      stickyRect.width -= w.value;
+      return {
+        rect: stickyRect,
+        scrollbarWidth: w.value,
+      };
+    }
+  );
+
+  // Take a snapshot where the position:sticky element is initially painted.
+  const reference = await getSnapshot(rect);
+
+  let mouseX = window.innerWidth - scrollbarWidth / 2;
+  let mouseY = tab.linkedBrowser.getBoundingClientRect().y + 5;
+
+  // Scroll fast to cause checkerboarding multiple times.
+  const dragFinisher = await promiseNativeMouseDrag(
+    window,
+    mouseX,
+    mouseY,
+    0,
+    window.innerHeight,
+    100
+  );
+
+  // On debug builds there seems to be no chance that the content process gets
+  // painted during above promiseNativeMouseDrag call, wait two frames to make
+  // sure it happens so that this test is likely able to fail without proper
+  // fix.
+  if (AppConstants.DEBUG) {
+    await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+      await content.wrappedJSObject.promiseFrame(content.window);
+      await content.wrappedJSObject.promiseFrame(content.window);
+    });
+  }
+
+  // Take a snapshot again where the position:sticky element should be painted.
+  const snapshot = await getSnapshot(rect);
+
+  await dragFinisher();
+
+  is(
+    snapshot,
+    reference,
+    "The position:sticky element should stay at the " +
+      "same place after scrolling on heavy load"
+  );
+
+  BrowserTestUtils.removeTab(tab);
+});