Method flushPromises

frontend/src/TestUtils.ts:37–53

* Flushes all already queued promises and returns a promise. Note this will * only work if the promises have already been queued, so it cannot be used to * wait on a promise that hasn't been dispatched yet.

()

   * wait on a promise that hasn't been dispatched yet.
   */
  public static async flushPromises(): Promise<void> {
    const testApi = getTestApi();
    if (
      typeof testApi.isMockFunction === 'function' &&
      testApi.isMockFunction(setTimeout) &&
      typeof testApi.advanceTimersByTime === 'function'
    ) {
      // Fake timers won't advance unless we flush them explicitly.
      testApi.advanceTimersByTime(0);
      await Promise.resolve();
      testApi.advanceTimersByTime(0);
      await Promise.resolve();
      return;
    }
    await new Promise(resolve => setTimeout(resolve, 0));
    await new Promise(resolve => setTimeout(resolve, 0));
  }

  /**
   * Adds a one-time mock implementation to the provided spy that mimics an error