stubbing services notes

Author: mike-north

notes/11-stubbing-services-in-tests.md

@@ -0,0 +1,53 @@
+# Stubbing Services in Tests
+
+We have a problem: our tests only pass, when we're logged in with a particular userId -- because they're actually reading/writing to cookies! This is a leak, and we need to fix it
+
+Create a file in your tests folder like [`tests/test-helpers/auth-service.js`](../tests/test-helpers/auth-service.js), where we'll put our "stub" service that will be used in place of the real one during tests
+
+```js
+import Service, { inject as service } from '@ember/service';
+import Router from '@ember/routing/router';
+import { tracked } from '@glimmer/tracking';
+
+export default class StubbedAuthService extends Service {
+  /**
+   * @type {Router}
+   */
+  @service router;
+  /**
+   * @type {string}
+   */
+  @tracked currentUserId = null;
+
+  get isAuthenticated() {
+    return !!this.currentUserId;
+  }
+
+  loginWithUserId(id) {
+    this.currentUserId = id;
+    this.router.transitionTo('teams');
+  }
+}
+```
+
+Now we just need to install it. Go to [`tests/integration/components/team-sidebar-test.js`](../tests/integration/components/team-sidebar-test.js) and begin by importing the stub service
+
+```js
+import StubbedAuthService from 'shlack/tests/test-helpers/auth-service';
+```
+
+Now we just need to "register" the service before each test, ensuring our test-appropriate one is used in place of the real one. Put this code in the test module, but before any tests.
+
+```js
+hooks.beforeEach(function() {
+  this.owner.register('service:auth', StubbedAuthService);
+});
+```
+
+Finally, at the beginning of the test, set the state of the service according to our needs
+
+```js
+this.owner.lookup('service:auth').currentUserId = 'LOL';
+```
+
+Make an appropriate adjustment to the assertion value, taking the userId into account and you should be good to go!