title: Setup result for call to extension method
body: <p>I'm trying to <code>Setup</code> the return of a call to an extension method and am receiving:</p>
  
  <p><code>SetUp : System.NotSupportedException : Expression references a method that does not belong to the mocked object: m =&gt; m.Cache.GetOrStore&lt;String&gt;("CacheKey", () =&gt; "Foo", 900)</code></p>
  
  <p>It seems to have a problem with referencing the <code>GetOrStore</code> method on the Cache object which is an extension method.</p>
  
  <p>The code compiles but the test fails with this exception.</p>
  
  <p>What do I need to do to setup the result of an extension method like this?</p>