diff -r 000000000000 -r 6474c204b198 browser/components/sessionstore/test/unit/test_backup.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/sessionstore/test/unit/test_backup.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,42 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+
+let toplevel = this;
+Cu.import("resource://gre/modules/osfile.jsm");
+
+function run_test() {
+  do_get_profile();
+  Cu.import("resource:///modules/sessionstore/SessionFile.jsm", toplevel);
+  pathStore = OS.Path.join(OS.Constants.Path.profileDir, "sessionstore.js");
+  run_next_test();
+}
+
+let pathStore;
+function pathBackup(ext) {
+  return OS.Path.join(OS.Constants.Path.profileDir, "sessionstore.bak" + ext);
+}
+
+// Ensure that things proceed smoothly if there is no file to back up
+add_task(function test_nothing_to_backup() {
+  yield SessionFile.createBackupCopy("");
+});
+
+// Create a file, back it up, remove it
+add_task(function test_do_backup() {
+  let content = "test_1";
+  let ext = ".upgrade_test_1";
+  yield OS.File.writeAtomic(pathStore, content, {tmpPath: pathStore + ".tmp"});
+
+  do_print("Ensuring that the backup is created");
+  yield SessionFile.createBackupCopy(ext);
+  do_check_true((yield OS.File.exists(pathBackup(ext))));
+
+  let data = yield OS.File.read(pathBackup(ext));
+  do_check_eq((new TextDecoder()).decode(data), content);
+
+  do_print("Ensuring that we can remove the backup");
+  yield SessionFile.removeBackupCopy(ext);
+  do_check_false((yield OS.File.exists(pathBackup(ext))));
+});
+