title: Flutter/Dart wait for a few seconds in unit testing
body: <p>I am writing a timer app. In unit testing how do I wait for few seconds to test if my timer is working properly?</p>
  
  <pre><code>// I want something like this.
  test("Testing timer", () {
      int startTime = timer.seconds;
      timer.start();
  
      // do something to wait for 2 seconds
  
      expect(timer.seconds, startTime - 2);
  
  });
  </code></pre>