title: Stubbing jQuery.fn method works fine in Chrome and Firefox, IE8 fails
body: <p>I am writing a series of tests using sinon stubs with QUnit. The methods tested have a dependency of custom plugin we will call Foo, which I am stubbing out as such:</p>
  
  <pre><code>// setup
  var stub = this.stub(jQuery.fn, "Foo").returns("");
  
  // run
  someProprietyMethod();
  
  // assertions
  equal(stub.args.length, 3);
  equal(stub.args[0], "bar");
  equal(stub.thisValues[0], "#some-selector");
  // other assertions
  </code></pre>
  
  <p>I find using the sinon stubs very easy and intuitive compared to manually creating stubs. The problem is that this works fine in Chrome and Firefox, but not IE8. </p>
  
  <p>For IE8 in the test result I get:</p>
  
  <pre><code>Died on test #1 undefined: Object doesn't support this property or method
  </code></pre>
  
  <p>Placing some debugging breadcrumbs in the tested code, it looks like $().Foo and $.fn.Foo are both seen as methods, but the test stops running after $("#some-selector").Foo() is called, when run in IE8.</p>