/**
 * Wraps a test function in an asynchronous test zone. The test will automatically
 * complete when all asynchronous calls within this zone are done. Can be used
 * to wrap an {@link inject} call.
 *
 * Example:
 *
 * ```
 * it('...', async(inject([AClass], (object) => {
 *   object.doSomething.then(() => {
 *     expect(...);
 *   })
 * });
 * ```
 */
export function async(fn: Function): Function {
  return () => {
    return new Promise<void>((finishCallback, failCallback) => {
      var AsyncTestZoneSpec = Zone['AsyncTestZoneSpec'];
      var testZoneSpec = new AsyncTestZoneSpec(finishCallback, failCallback, 'test');
      var testZone = Zone.current.fork(testZoneSpec);
      return testZone.run(fn);
    });
  }
}