test(docs-infra): add unit tests for rx-library examples (#38905)

This commit adds missing unit tests for all rx-library examples from the docs.

Closes #28017

PR Close #38905

aio/content/examples/rx-library/src/simple-creation.spec.ts

@@ -0,0 +1,14 @@
+import { of } from 'rxjs';
+import { docRegionAjax } from './simple-creation';
+
+describe('ajax', () => {
+  it('should make a request and console log the status and response', () => {
+    const console = {log: jasmine.createSpy('log')};
+    const ajax = jasmine.createSpy('ajax').and.callFake((url: string) => {
+      return of({status: 200, response: 'foo bar'});
+    });
+
+    docRegionAjax(console, ajax);
+    expect(console.log).toHaveBeenCalledWith(200, 'foo bar');
+  });
+});