feat(core): add support for using async/await with Jasmine (#24637)

Example:
```
it('...', await(async() => {
  doSomething();
  await asyncFn();
  doSomethingAfter();
}));
```

PR Close #24637

packages/core/testing/src/jasmine_await.ts

@@ -0,0 +1,34 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+/**
+ * Converts an `async` function, with `await`, into a function which is compatible with Jasmine test
+ * framework.
+ *
+ * For asynchronous function blocks, Jasmine expects `it` (and friends) to take a function which
+ * takes a `done` callback. (Jasmine does not understand functions which return `Promise`.) The
+ * `jasmineAwait()` wrapper converts the test function returning `Promise` into a function which
+ * Jasmine understands.
+ *
+ *
+ * Example:
+ * ```
+ * it('...', jasmineAwait(async() => {
+ *   doSomething();
+ *   await asyncFn();
+ *   doSomethingAfter();
+ * }));
+ * ```
+ *
+ */
+export function jasmineAwait(fn: () => Promise<any>):
+    (done: {(): void; fail: (message?: Error | string) => void;}) => void {
+  return function(done: {(): void; fail: (message?: Error | string) => void;}) {
+    fn().then(done, done.fail);
+  };
+}

packages/core/testing/src/testing.ts

@@ -13,6 +13,7 @@
  */
 
 export * from './async';
+export * from './jasmine_await';
 export * from './component_fixture';
 export * from './fake_async';
 export * from './test_bed';