diff -r 000000000000 -r 6474c204b198 toolkit/components/osfile/tests/xpcshell/head.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/osfile/tests/xpcshell/head.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,86 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+let {utils: Cu, interfaces: Ci} = Components;
+
+let {OS} = Cu.import("resource://gre/modules/osfile.jsm", {});
+let {Services} = Cu.import("resource://gre/modules/Services.jsm", {});
+let {Promise} = Cu.import("resource://gre/modules/Promise.jsm", {});
+let {Task} = Cu.import("resource://gre/modules/Task.jsm", {});
+let {FileUtils} = Cu.import("resource://gre/modules/FileUtils.jsm", {});
+let {NetUtil} = Cu.import("resource://gre/modules/NetUtil.jsm", {});
+
+Services.prefs.setBoolPref("toolkit.osfile.log", true);
+
+/**
+ * As add_task, but execute the test both with native operations and
+ * without.
+ */
+function add_test_pair(generator) {
+  add_task(function*() {
+    do_print("Executing test " + generator.name + " with native operations");
+    Services.prefs.setBoolPref("toolkit.osfile.native", true);
+    return Task.spawn(generator);
+  });
+  add_task(function*() {
+    do_print("Executing test " + generator.name + " without native operations");
+    Services.prefs.setBoolPref("toolkit.osfile.native", false);
+    return Task.spawn(generator);
+  });
+}
+
+/**
+ * Fetch asynchronously the contents of a file using xpcom.
+ *
+ * Used for comparing xpcom-based results to os.file-based results.
+ *
+ * @param {string} path The _absolute_ path to the file.
+ * @return {promise}
+ * @resolves {string} The contents of the file.
+ */
+function reference_fetch_file(path, test) {
+  do_print("Fetching file " + path);
+  let deferred = Promise.defer();
+  let file = new FileUtils.File(path);
+  NetUtil.asyncFetch(file,
+    function(stream, status) {
+      if (!Components.isSuccessCode(status)) {
+        deferred.reject(status);
+        return;
+      }
+      let result, reject;
+      try {
+        result = NetUtil.readInputStreamToString(stream, stream.available());
+      } catch (x) {
+        reject = x;
+      }
+      stream.close();
+      if (reject) {
+        deferred.reject(reject);
+      } else {
+        deferred.resolve(result);
+      }
+  });
+  return deferred.promise;
+};
+
+/**
+ * Compare asynchronously the contents two files using xpcom.
+ *
+ * Used for comparing xpcom-based results to os.file-based results.
+ *
+ * @param {string} a The _absolute_ path to the first file.
+ * @param {string} b The _absolute_ path to the second file.
+ *
+ * @resolves {null}
+ */
+function reference_compare_files(a, b, test) {
+  return Task.spawn(function*() {
+    do_print("Comparing files " + a + " and " + b);
+    let a_contents = yield reference_fetch_file(a, test);
+    let b_contents = yield reference_fetch_file(b, test);
+    do_check_eq(a_contents, b_contents);
+  });
+};