Use fake date in spec environment

- This makes sure the fake date is
  truly applied everywhere and
  fixes an issue where jsdom was
  not aware of the fake date.

spec/frontend/__helpers__/fake_date.js

 // Frida Kahlo's birthday (6 = July)
-export const DEFAULT_ARGS = [2020, 6, 6];
+const DEFAULT_ARGS = [2020, 6, 6];
 
 const RealDate = Date;
 
 const isMocked = (val) => Boolean(val.mock);
 
-export const createFakeDateClass = (ctorDefault) => {
+const createFakeDateClass = (ctorDefault) => {
   const FakeDate = new Proxy(RealDate, {
     construct: (target, argArray) => {
       const ctorArgs = argArray.length ? argArray : ctorDefault;
@@ -39,11 +39,20 @@ export const createFakeDateClass = (ctorDefault) => {
   return FakeDate;
 };
 
-export const useFakeDate = (...args) => {
+const useFakeDate = (...args) => {
   const FakeDate = createFakeDateClass(args.length ? args : DEFAULT_ARGS);
   global.Date = FakeDate;
 };
 
-export const useRealDate = () => {
+const useRealDate = () => {
   global.Date = RealDate;
 };
+
+// We use commonjs so that the test environment module can pick this up
+// eslint-disable-next-line import/no-commonjs
+module.exports = {
+  useFakeDate,
+  useRealDate,
+  DEFAULT_ARGS,
+  createFakeDateClass,
+};

spec/frontend/environment.js

@@ -4,6 +4,7 @@ const path = require('path');
 const { ErrorWithStack } = require('jest-util');
 const JSDOMEnvironment = require('jest-environment-jsdom');
 const { TEST_HOST } = require('./__helpers__/test_constants');
+const { useFakeDate } = require('./__helpers__/fake_date');
 
 const ROOT_PATH = path.resolve(__dirname, '../..');
 
@@ -12,6 +13,9 @@ class CustomEnvironment extends JSDOMEnvironment {
     // Setup testURL so that window.location is setup properly
     super({ ...config, testURL: TEST_HOST }, context);
 
+    // This lets jsdom use the fake date for things like document.cookie
+    useFakeDate();
+
     Object.assign(context.console, {
       error(...args) {
         throw new ErrorWithStack(

spec/frontend/test_setup.js

@@ -21,8 +21,6 @@ process.on('unhandledRejection', global.promiseRejectionHandler);
 
 setupManualMocks();
 
-useFakeDate();
-
 afterEach(() =>
   // give Promises a bit more time so they fail the right test
   new Promise(setImmediate).then(() => {