title: How do you mock an IAsyncEnumerable?
body: <p>I want to unit test a method that calls another method of a service returning an <code>IAsyncEnumerable&lt;T&gt;</code>.
  I have created a a mock of my service <code>Mock&lt;MyService&gt;</code> and I want to setUp this mock but I don't know how to do that. Is it possible ? Are there other ways of unit testing a method that calls something retuning an <code>IAsyncEnumerable</code> </p>
  
  <pre class="lang-cs prettyprint-override"><code>public async Task&lt;List&lt;String&gt;&gt; MyMethodIWantToTest()
  {
    var results = new List&lt;string&gt;();
    await foreach(var item in _myService.CallSomethingReturningAsyncStream())
    {
      results.Add(item);
    }
    return results;
  }
  </code></pre>