1 files changed, 62 insertions, 0 deletions
diff --git a/browser/base/content/test/general/browser_lastAccessedTab.js b/browser/base/content/test/general/browser_lastAccessedTab.js
new file mode 100644
index 0000000000..631fcb3bfe
--- /dev/null
+++ b/browser/base/content/test/general/browser_lastAccessedTab.js
@@ -0,0 +1,62 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+/* eslint-disable mozilla/no-arbitrary-setTimeout */
+
+// gBrowser.selectedTab.lastAccessed and Date.now() called from this test can't
+// run concurrently, and therefore don't always match exactly.
+const CURRENT_TIME_TOLERANCE_MS = 15;
+
+function isCurrent(tab, msg) {
+  const DIFF = Math.abs(Date.now() - tab.lastAccessed);
+  ok(DIFF <= CURRENT_TIME_TOLERANCE_MS, msg + " (difference: " + DIFF + ")");
+}
+
+function nextStep(fn) {
+  setTimeout(fn, CURRENT_TIME_TOLERANCE_MS + 10);
+}
+
+var originalTab;
+var newTab;
+
+function test() {
+  waitForExplicitFinish();
+  // This test assumes that time passes between operations. But if the precision
+  // is low enough, and the test fast enough, an operation, and a successive call
+  // to Date.now() will have the same time value.
+  SpecialPowers.pushPrefEnv(
+    { set: [["privacy.reduceTimerPrecision", false]] },
+    function () {
+      originalTab = gBrowser.selectedTab;
+      nextStep(step2);
+    }
+  );
+}
+
+function step2() {
+  isCurrent(originalTab, "selected tab has the current timestamp");
+  newTab = BrowserTestUtils.addTab(gBrowser, "about:blank", {
+    skipAnimation: true,
+  });
+  nextStep(step3);
+}
+
+function step3() {
+  ok(newTab.lastAccessed < Date.now(), "new tab hasn't been selected so far");
+  gBrowser.selectedTab = newTab;
+  isCurrent(newTab, "new tab has the current timestamp after being selected");
+  nextStep(step4);
+}
+
+function step4() {
+  ok(
+    originalTab.lastAccessed < Date.now(),
+    "original tab has old timestamp after being deselected"
+  );
+  isCurrent(
+    newTab,
+    "new tab has the current timestamp since it's still selected"
+  );
+
+  gBrowser.removeTab(newTab);
+  finish();
+}