Fix time-dependent test failure in release_block_spec.js

This test was using timeago.js to show amount of time elapsed since the
release date. Since timeago.js uses Date() to determine the current
timestamp, we can just mock that value to ensure consistent results.

Closes https://gitlab.com/gitlab-org/gitlab/issues/35019

spec/frontend/releases/list/components/release_block_spec.js

@@ -39,13 +39,25 @@ describe('Release block', () => {
 
   const milestoneListLabel = () => wrapper.find('.js-milestone-list-label');
   const editButton = () => wrapper.find('.js-edit-button');
+  const RealDate = Date;
 
   beforeEach(() => {
+    // timeago.js calls Date(), so let's mock that case to avoid time-dependent test failures.
+    const constantDate = new Date('2019-10-25T00:12:00');
+
+    /* eslint no-global-assign:off */
+    global.Date = jest.fn((...props) =>
+      props.length ? new RealDate(...props) : new RealDate(constantDate),
+    );
+
+    Object.assign(Date, RealDate);
+
     releaseClone = JSON.parse(JSON.stringify(release));
   });
 
   afterEach(() => {
     wrapper.destroy();
+    global.Date = RealDate;
   });
 
   describe('with default props', () => {