refactor(docs-infra): take advantage of latest Jasmine features in preview server tests (#36837)

This commit updates the preview server tests to take advantage of
features supported in the latest version of Jasmine that were not
supported when the rests were first written.

Changes include:

- Use [async/await] in tests.
- Use the new [toBeInstanceOf()] and [toHaveBeenCalledBefore()] matchers.
- Use the new [toBeResolved()] and [toBeRejected()] async matchers (and
  their variants).
- Use the new [withArgs()] method of `Spy` to simplify "trained"
  responses.
- Use the new [resolveTo()]/[rejectWith()] methods of `SpyStrategy` (and
  their variants) to simplify promise-based spies.
- Implement custom async matchers (via [addAsyncMatchers()]) to simplify
  certain tests.

[addAsyncMatchers()]: https://jasmine.github.io/api/3.5/jasmine.html#.addAsyncMatchers
[async/await]: https://jasmine.github.io/tutorials/async
[rejectWith()]: https://jasmine.github.io/api/3.5/SpyStrategy.html#rejectWith
[resolveTo()]: https://jasmine.github.io/api/3.5/SpyStrategy.html#resolveTo
[toBeInstanceOf()]: https://jasmine.github.io/api/3.5/matchers.html#toBeInstanceOf
[toBeRejected()]: https://jasmine.github.io/api/3.5/async-matchers.html#toBeRejected
[toBeResolved()]: https://jasmine.github.io/api/3.5/async-matchers.html#toBeResolved
[toHaveBeenCalledBefore()]: https://jasmine.github.io/api/3.5/matchers.html#toHaveBeenCalledBefore
[withArgs()]: https://jasmine.github.io/api/3.5/Spy.html#withArgs

PR Close #36837

aio/aio-builds-setup/dockerbuild/scripts-js/test/common/github-pull-requests.spec.ts

@@ -53,21 +53,15 @@ describe('GithubPullRequests', () => {
     });
 
 
-    it('should reject if the request fails', done => {
-      githubApi.post.and.callFake(() => Promise.reject('Test'));
-      prs.addComment(42, 'body').catch(err => {
-        expect(err).toBe('Test');
-        done();
-      });
+    it('should reject if the request fails', async () => {
+      githubApi.post.and.rejectWith('Test');
+      await expectAsync(prs.addComment(42, 'body')).toBeRejectedWith('Test');
     });
 
 
-    it('should resolve with the data from the Github POST', done => {
+    it('should resolve with the data from the Github POST', async () => {
       githubApi.post.and.resolveTo('Test');
-      prs.addComment(42, 'body').then(data => {
-        expect(data).toBe('Test');
-        done();
-      });
+      await expectAsync(prs.addComment(42, 'body')).toBeResolvedTo('Test');
     });
 
   });
@@ -87,13 +81,11 @@ describe('GithubPullRequests', () => {
     });
 
 
-    it('should resolve with the data returned from GitHub', done => {
+    it('should resolve with the data returned from GitHub', async () => {
       const expected: any = {number: 42};
-      githubApi.get.and.callFake(() => Promise.resolve(expected));
-      prs.fetch(42).then(data => {
-        expect(data).toEqual(expected);
-        done();
-      });
+      githubApi.get.and.resolveTo(expected);
+
+      await expectAsync(prs.fetch(42)).toBeResolvedTo(expected);
     });
 
   });
@@ -152,13 +144,11 @@ describe('GithubPullRequests', () => {
     });
 
 
-    it('should resolve with the data returned from GitHub', done => {
+    it('should resolve with the data returned from GitHub', async () => {
       const expected: any = [{sha: 'ABCDE', filename: 'a/b/c'}, {sha: '12345', filename: 'x/y/z'}];
-      githubApi.getPaginated.and.callFake(() => Promise.resolve(expected));
-      prs.fetchFiles(42).then(data => {
-        expect(data).toEqual(expected);
-        done();
-      });
+      githubApi.getPaginated.and.resolveTo(expected);
+
+      await expectAsync(prs.fetchFiles(42)).toBeResolvedTo(expected);
     });
 
   });