title: Dart: How I can get length of Stream?
body: <p>I want to get length of BehaviorSubject's stream, but I can't get it.</p>
  
  <pre><code>test('get stream length', ()async{
      BehaviorSubject&lt;int&gt; subject = new BehaviorSubject(seedValue: 0);
  
      var act = await subject.stream.length;
  
      expect(act, 1);
    }); 
  </code></pre>
  
  <p>How I can get this length?</p>