1 files changed, 116 insertions, 0 deletions
diff --git a/browser/components/sessionstore/test/browser_merge_closed_tabs.js b/browser/components/sessionstore/test/browser_merge_closed_tabs.js
new file mode 100644
index 0000000000..2c6a946cdf
--- /dev/null
+++ b/browser/components/sessionstore/test/browser_merge_closed_tabs.js
@@ -0,0 +1,116 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * This test ensures that closed tabs are merged when restoring
+ * a window state without overwriting tabs.
+ */
+add_task(async function () {
+  const initialState = {
+    windows: [
+      {
+        tabs: [
+          { entries: [{ url: "about:blank", triggeringPrincipal_base64 }] },
+        ],
+        _closedTabs: [
+          {
+            state: {
+              entries: [
+                { ID: 1000, url: "about:blank", triggeringPrincipal_base64 },
+              ],
+            },
+          },
+          {
+            state: {
+              entries: [
+                { ID: 1001, url: "about:blank", triggeringPrincipal_base64 },
+              ],
+            },
+          },
+        ],
+      },
+    ],
+  };
+
+  const restoreState = {
+    windows: [
+      {
+        tabs: [
+          { entries: [{ url: "about:robots", triggeringPrincipal_base64 }] },
+        ],
+        _closedTabs: [
+          {
+            state: {
+              entries: [
+                { ID: 1002, url: "about:robots", triggeringPrincipal_base64 },
+              ],
+            },
+          },
+          {
+            state: {
+              entries: [
+                { ID: 1003, url: "about:robots", triggeringPrincipal_base64 },
+              ],
+            },
+          },
+          {
+            state: {
+              entries: [
+                { ID: 1004, url: "about:robots", triggeringPrincipal_base64 },
+              ],
+            },
+          },
+        ],
+      },
+    ],
+  };
+
+  const maxTabsUndo = 4;
+  Services.prefs.setIntPref("browser.sessionstore.max_tabs_undo", maxTabsUndo);
+
+  // Open a new window and restore it to an initial state.
+  let win = await promiseNewWindowLoaded({ private: false });
+  await setWindowState(win, initialState, true);
+  is(
+    SessionStore.getClosedTabCountForWindow(win),
+    2,
+    "2 closed tabs after restoring initial state"
+  );
+
+  // Restore the new state but do not overwrite existing tabs (this should
+  // cause the closed tabs to be merged).
+  await setWindowState(win, restoreState);
+
+  // Verify the windows closed tab data is correct.
+  let iClosed = initialState.windows[0]._closedTabs;
+  let rClosed = restoreState.windows[0]._closedTabs;
+  let cData = SessionStore.getClosedTabDataForWindow(win);
+
+  is(
+    cData.length,
+    Math.min(iClosed.length + rClosed.length, maxTabsUndo),
+    "Number of closed tabs is correct"
+  );
+
+  // When the closed tabs are merged the restored tabs are considered to be
+  // closed more recently.
+  for (let i = 0; i < cData.length; i++) {
+    if (i < rClosed.length) {
+      is(
+        cData[i].state.entries[0].ID,
+        rClosed[i].state.entries[0].ID,
+        "Closed tab entry matches"
+      );
+    } else {
+      is(
+        cData[i].state.entries[0].ID,
+        iClosed[i - rClosed.length].state.entries[0].ID,
+        "Closed tab entry matches"
+      );
+    }
+  }
+
+  // Clean up.
+  Services.prefs.clearUserPref("browser.sessionstore.max_tabs_undo");
+  await BrowserTestUtils.closeWindow(win);
+});