diff -r 000000000000 -r 6474c204b198 services/sync/modules-testing/fakeservices.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/services/sync/modules-testing/fakeservices.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,103 @@
+/* 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/. */
+
+"use strict";
+
+this.EXPORTED_SYMBOLS = [
+  "FakeCryptoService",
+  "FakeFilesystemService",
+  "FakeGUIDService",
+  "fakeSHA256HMAC",
+];
+
+const {utils: Cu} = Components;
+
+Cu.import("resource://services-sync/record.js");
+Cu.import("resource://services-sync/util.js");
+
+let btoa = Cu.import("resource://gre/modules/Log.jsm").btoa;
+
+this.FakeFilesystemService = function FakeFilesystemService(contents) {
+  this.fakeContents = contents;
+  let self = this;
+
+  Utils.jsonSave = function jsonSave(filePath, that, obj, callback) {
+    let json = typeof obj == "function" ? obj.call(that) : obj;
+    self.fakeContents["weave/" + filePath + ".json"] = JSON.stringify(json);
+    callback.call(that);
+  };
+
+  Utils.jsonLoad = function jsonLoad(filePath, that, cb) {
+    let obj;
+    let json = self.fakeContents["weave/" + filePath + ".json"];
+    if (json) {
+      obj = JSON.parse(json);
+    }
+    cb.call(that, obj);
+  };
+};
+
+this.fakeSHA256HMAC = function fakeSHA256HMAC(message) {
+   message = message.substr(0, 64);
+   while (message.length < 64) {
+     message += " ";
+   }
+   return message;
+}
+
+this.FakeGUIDService = function FakeGUIDService() {
+  let latestGUID = 0;
+
+  Utils.makeGUID = function makeGUID() {
+    return "fake-guid-" + latestGUID++;
+  };
+}
+
+/*
+ * Mock implementation of WeaveCrypto. It does not encrypt or
+ * decrypt, merely returning the input verbatim.
+ */
+this.FakeCryptoService = function FakeCryptoService() {
+  this.counter = 0;
+
+  delete Svc.Crypto;  // get rid of the getter first
+  Svc.Crypto = this;
+
+  CryptoWrapper.prototype.ciphertextHMAC = function ciphertextHMAC(keyBundle) {
+    return fakeSHA256HMAC(this.ciphertext);
+  };
+}
+FakeCryptoService.prototype = {
+
+  encrypt: function encrypt(clearText, symmetricKey, iv) {
+    return clearText;
+  },
+
+  decrypt: function decrypt(cipherText, symmetricKey, iv) {
+    return cipherText;
+  },
+
+  generateRandomKey: function generateRandomKey() {
+    return btoa("fake-symmetric-key-" + this.counter++);
+  },
+
+  generateRandomIV: function generateRandomIV() {
+    // A base64-encoded IV is 24 characters long
+    return btoa("fake-fake-fake-random-iv");
+  },
+
+  expandData: function expandData(data, len) {
+    return data;
+  },
+
+  deriveKeyFromPassphrase: function deriveKeyFromPassphrase(passphrase,
+                                                            salt, keyLength) {
+    return "some derived key string composed of bytes";
+  },
+
+  generateRandomBytes: function generateRandomBytes(byteCount) {
+    return "not-so-random-now-are-we-HA-HA-HA! >:)".slice(byteCount);
+  }
+};
+