title: Mocking Action<T> with NSubstitute
body: <p>A proxy for a webservice needs unit testing without - obviously - hitting the web service.</p>
  
  <p>This is the method I'd like to neuter - </p>
  
  <pre><code>public void Invoke(Action&lt;T&gt; action)
  {
      Task.Run(async ()=&gt; { await _invoker.Invoke(this, action); }).Wait();
  }
  </code></pre>
  
  <p>Is there any way to mock the Action parameter using NSubstitute?  I've been working along the lines of using </p>
  
  <pre><code>_proxy.When(x =&gt; x.Invoke($args_go_here)).Do(x =&gt; _counter++);
  </code></pre>
  
  <p>but I'm having real troubles formulating the Args expressions.  If I could simply create a mock with the Action signature and pass it in, life would be much simpler and more readable.</p>