Add a helper to spy on window.location

The window.location interface is read only in newer versions of jest.
This breaks our manual mocks / spys on that interface.

With a helper which replaces `window.location` with a mocked interface
we are able to circumvent that problem.

ee/spec/frontend/subscriptions/new/store/actions_spec.js

 import testAction from 'helpers/vuex_action_helper';
+import { useMockLocationHelper } from 'helpers/mock_window_location_helper';
 import MockAdapter from 'axios-mock-adapter';
 import axios from '~/lib/utils/axios_utils';
 import createFlash from '~/flash';
@@ -628,13 +629,13 @@ describe('Subscriptions Actions', () => {
   });
 
   describe('confirmOrderSuccess', () => {
+    useMockLocationHelper();
+
     const params = { location: 'http://example.com', plan_id: 'x', quantity: 10 };
 
     it('changes the window location', done => {
-      const spy = jest.spyOn(window.location, 'assign').mockImplementation();
-
       testAction(actions.confirmOrderSuccess, params, {}, [], [], () => {
-        expect(spy).toHaveBeenCalledWith('http://example.com');
+        expect(window.location.assign).toHaveBeenCalledWith('http://example.com');
         done();
       });
     });

spec/frontend/create_cluster/eks_cluster/store/actions_spec.js

 import testAction from 'helpers/vuex_action_helper';
+import { useMockLocationHelper } from 'helpers/mock_window_location_helper';
 import MockAdapter from 'axios-mock-adapter';
 import createState from '~/create_cluster/eks_cluster/store/state';
 import * as actions from '~/create_cluster/eks_cluster/store/actions';
@@ -251,12 +252,7 @@ describe('EKS Cluster Store Actions', () => {
   });
 
   describe('createClusterSuccess', () => {
-    beforeEach(() => {
-      jest.spyOn(window.location, 'assign').mockImplementation(() => {});
-    });
-    afterEach(() => {
-      window.location.assign.mockRestore();
-    });
+    useMockLocationHelper();
 
     it('redirects to the new cluster URL', () => {
       actions.createClusterSuccess(null, newClusterUrl);

spec/frontend/helpers/mock_window_location_helper.js

+/**
+ * Manage the instance of a custom `window.location`
+ *
+ * This only encapsulates the setup / teardown logic so that it can easily be
+ * reused with different implementations (i.e. a spy or a [fake][1])
+ *
+ * [1]: https://stackoverflow.com/a/41434763/1708147
+ *
+ * @param {() => any} fn Function that returns the object to use for window.location
+ */
+const useMockLocation = fn => {
+  const origWindowLocation = window.location;
+  let currentWindowLocation;
+
+  Object.defineProperty(window, 'location', {
+    get: () => currentWindowLocation,
+  });
+
+  beforeEach(() => {
+    currentWindowLocation = fn();
+  });
+
+  afterEach(() => {
+    currentWindowLocation = origWindowLocation;
+  });
+};
+
+/**
+ * Create an object with the location interface but `jest.fn()` implementations.
+ */
+export const createWindowLocationSpy = () => {
+  return {
+    assign: jest.fn(),
+    reload: jest.fn(),
+    replace: jest.fn(),
+    toString: jest.fn(),
+  };
+};
+
+/**
+ * Before each test, overwrite `window.location` with a spy implementation.
+ */
+export const useMockLocationHelper = () => useMockLocation(createWindowLocationSpy);

spec/frontend/helpers/set_window_location_helper_spec.js

@@ -33,7 +33,7 @@ describe('setWindowLocation', () => {
   it.each([null, 1, undefined, false, '', 'gitlab.com'])(
     'throws an error when called with an invalid url: "%s"',
     invalidUrl => {
-      expect(() => setWindowLocation(invalidUrl)).toThrow(new TypeError('Invalid URL'));
+      expect(() => setWindowLocation(invalidUrl)).toThrow(/Invalid URL/);
       expect(window.location).toBe(originalLocation);
     },
   );

spec/frontend/ide/stores/actions/project_spec.js

@@ -12,7 +12,8 @@ import {
 } from '~/ide/stores/actions';
 import service from '~/ide/services';
 import api from '~/api';
-import testAction from '../../../helpers/vuex_action_helper';
+import testAction from 'helpers/vuex_action_helper';
+import { useMockLocationHelper } from 'helpers/mock_window_location_helper';
 
 const TEST_PROJECT_ID = 'abc/def';
 
@@ -116,6 +117,8 @@ describe('IDE store project actions', () => {
   });
 
   describe('createNewBranchFromDefault', () => {
+    useMockLocationHelper();
+
     beforeEach(() => {
       jest.spyOn(api, 'createBranch').mockResolvedValue();
     });
@@ -170,8 +173,6 @@ describe('IDE store project actions', () => {
     });
 
     it('reloads window', done => {
-      jest.spyOn(window.location, 'reload').mockImplementation();
-
       createNewBranchFromDefault(
         {
           state: {

spec/frontend/sidebar/confidential_issue_sidebar_spec.js

@@ -6,11 +6,14 @@ import SidebarService from '~/sidebar/services/sidebar_service';
 import createFlash from '~/flash';
 import RecaptchaModal from '~/vue_shared/components/recaptcha_modal.vue';
 import createStore from '~/notes/stores';
+import { useMockLocationHelper } from 'helpers/mock_window_location_helper';
 
 jest.mock('~/flash');
 jest.mock('~/sidebar/services/sidebar_service');
 
 describe('Confidential Issue Sidebar Block', () => {
+  useMockLocationHelper();
+
   let wrapper;
 
   const findRecaptchaModal = () => wrapper.find(RecaptchaModal);
@@ -43,10 +46,6 @@ describe('Confidential Issue Sidebar Block', () => {
     });
   };
 
-  beforeEach(() => {
-    jest.spyOn(window.location, 'reload').mockImplementation();
-  });
-
   afterEach(() => {
     wrapper.destroy();
   });