diff -r 000000000000 -r 6474c204b198 js/xpconnect/tests/unit/test_file2.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/xpconnect/tests/unit/test_file2.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,69 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const Ci = Components.interfaces;
+
+function run_test() {
+  // throw if anything goes wrong
+
+  // find the current directory path
+  var file = Components.classes["@mozilla.org/file/directory_service;1"]
+             .getService(Ci.nsIProperties)
+             .get("CurWorkD", Ci.nsIFile);
+  file.append("xpcshell.ini");
+
+  // should be able to construct a file
+  var f1 = File(file.path);
+  // with either constructor syntax
+  var f2 = new File(file.path);
+  // and with nsIFiles
+  var f3 = File(file);
+  var f4 = new File(file);
+
+  // do some tests
+  do_check_true(f1 instanceof Ci.nsIDOMFile, "Should be a DOM File");
+  do_check_true(f2 instanceof Ci.nsIDOMFile, "Should be a DOM File");
+  do_check_true(f3 instanceof Ci.nsIDOMFile, "Should be a DOM File");
+  do_check_true(f4 instanceof Ci.nsIDOMFile, "Should be a DOM File");
+
+  do_check_true(f1.name == "xpcshell.ini", "Should be the right file");
+  do_check_true(f2.name == "xpcshell.ini", "Should be the right file");
+  do_check_true(f3.name == "xpcshell.ini", "Should be the right file");
+  do_check_true(f4.name == "xpcshell.ini", "Should be the right file");
+
+  do_check_true(f1.type == "", "Should be the right type");
+  do_check_true(f2.type == "", "Should be the right type");
+  do_check_true(f3.type == "", "Should be the right type");
+  do_check_true(f4.type == "", "Should be the right type");
+
+  var threw = false;
+  try {
+    // Needs a ctor argument
+    var f7 = File();
+  } catch (e) {
+    threw = true;
+  }
+  do_check_true(threw, "No ctor arguments should throw");
+
+  var threw = false;
+  try {
+    // Needs a valid ctor argument
+    var f7 = File(Date(132131532));
+  } catch (e) {
+    threw = true;
+  }
+  do_check_true(threw, "Passing a random object should fail");
+
+  var threw = false
+  try {
+    // Directories fail
+    var dir = Components.classes["@mozilla.org/file/directory_service;1"]
+                        .getService(Ci.nsIProperties)
+                        .get("CurWorkD", Ci.nsIFile);
+    var f7 = File(dir)
+  } catch (e) {
+    threw = true;
+  }
+  do_check_true(threw, "Can't create a File object for a directory");
+}