Unit tests for addon/lib/metrics.js

- Use the downloaded Firefox for both integration and add-on unit tests.

- Switch from Ci.import() to require() for some JS modules in
  addon/lib/metrics.js, making them replaceable with mock APIs

- New tests in addon/test/test-metrics.js

- Include add-on testing in bin/circleci/build-addon.sh

- Utilities for mocking out API functions and monitoring calls

- Custom module loader to substitute mock modules on require() calls in
  the test subject module

Issue mozilla#1220

addon/README.md

@@ -55,6 +55,16 @@ A relatively easy path for working on this addon involves the following steps:
 
 For UI hacking you can run `npm run watch-ui` to easily debug `lib/templates.js` and `data/panel.css`
 
+## tests
+
+Unit tests for the add-on are run via `jpm` as an `npm` script:
+
+```
+npm test -- --binary=/Applications/Nightly.app/Contents/MacOS/firefox-bin
+```
+
+Look in the `test` directory for examples of tests.
+
 ## running once for testing
 
 * Install [Firefox Beta][fxbeta]

addon/lib/metrics.js

@@ -4,14 +4,9 @@
  * http://mozilla.org/MPL/2.0/.
  */
 
-/* global TelemetryController, Services */
-
-const {Cu} = require('chrome');
-
-Cu.import('resource://gre/modules/Services.jsm');
-Cu.import('resource://gre/modules/TelemetryController.jsm');
-
 const { AddonManager } = require('resource://gre/modules/AddonManager.jsm');
+const { Services } = require('resource://gre/modules/Services.jsm');
+const { TelemetryController } = require('resource://gre/modules/TelemetryController.jsm');
 const Events = require('sdk/system/events');
 const PrefsService = require('sdk/preferences/service');
 const self = require('sdk/self');

addon/package.json

@@ -19,6 +19,7 @@
   "updateURL": "https://testpilot.firefox.com/static/addon/update.rdf",
   "updateLink": "https://testpilot.firefox.com/static/addon/addon.xpi",
   "scripts": {
+    "test": "./node_modules/.bin/jpm test --verbose",
     "start": "npm run watch",
     "once": "jpm run -b beta --prefs dev-prefs.json",
     "watch": "jpm watchpost --post-url http://127.0.0.1:8888",

addon/test/lib/mock-utils.js

@@ -0,0 +1,103 @@
+const { Loader, Require, unload,
+        override, descriptor } = require('toolkit/loader');
+const { ensure } = require('sdk/system/unload');
+
+let debug = false;
+
+exports.setDebug = (flag) => debug = flag;
+
+exports.callback = function(name) {
+  let callState = [];
+  let implementCb = null;
+
+  const fn = function() {
+    const args = Array.prototype.slice.call(arguments);
+    args.timestamp = Date.now();
+    if (debug) {
+      console.log(name, args);  // eslint-disable-line no-console
+    }
+    callState.push(args);
+    if (implementCb) {
+      return implementCb.apply(fn, args);
+    }
+  };
+
+  fn.reset = () => {
+    callState = [];
+    implementCb = null;
+  };
+  fn.calls = () => callState;
+  fn.implement = cb => implementCb = cb;
+
+  return fn;
+};
+
+exports.callbacks = function(spec) {
+  const out = {};
+  Object.keys(spec).forEach(prefix => {
+    out[prefix] = {};
+    spec[prefix].forEach(name => {
+      out[prefix][name] = exports.callback(prefix + '.' + name);
+    });
+  });
+  return out;
+};
+
+exports.resetCallbacks = function(callbacks) {
+  Object.keys(callbacks).forEach(prefix => {
+    const items = callbacks[prefix];
+    Object.keys(items).forEach(name => items[name].reset());
+  });
+};
+
+// Build a custom module loader that substitutes mock modules for the test
+// subject's require() calls.
+exports.loader = function(testModule, subjectPath, modules) {
+  const loaderOptions = require('@loader/options');
+
+  // Get a handle on the original resolver created by default in Loader.
+  const realResolve = loaderOptions.isNative ?
+      (id, requirer) => Loader.nodeResolve(id, requirer, {rootURI: loaderOptions.rootURI}) :
+      Loader.resolve;
+
+  // Custom resolver that substitutes mock modules, but only when the test
+  // subject module is asking for them.
+  const mockResolve = (id, requirer) => {
+    let resolvedPath = realResolve(id, requirer);
+    // Only trigger mock module substitution for the test subject
+    if (requirer === subjectPath) {
+      // If the real resolver came up with no mapping, use the original ID
+      if (!resolvedPath) { resolvedPath = id; }
+      // If the path is in our set of mock substitutions, use the prefix.
+      if (resolvedPath in modules) {
+        resolvedPath = 'mock:' + resolvedPath;
+        // Announce the substitution if debug is on.
+        if (debug) {
+          console.log('Substituting mock', requirer, '<=', id);  // eslint-disable-line no-console
+        }
+      }
+    }
+    return resolvedPath;
+  };
+
+  // Prefix all the supplied mock modules for conditional injection
+  const mockModules = {};
+  Object.keys(modules).forEach(path => {
+    mockModules['mock:' + path] = modules[path];
+  });
+
+  // Build and return the mock module loader
+  const loader = Loader(override(  // eslint-disable-line new-cap
+    loaderOptions,
+    {modules: mockModules, resolve: mockResolve}
+  ));
+
+  const mockLoader = Object.create(loader, descriptor({
+    require: Require(loader, testModule),  // eslint-disable-line new-cap
+    unload: reason => unload(loader, reason)
+  }));
+
+  ensure(mockLoader);
+
+  return mockLoader;
+};