title: MEF Composition Error, Export doesn't work as it should
body: <p>this is my form which should display the result from my imported class: </p>
  
  <pre><code>public partial class Form1 : Form
  {
      [Import(typeof(ITests))]
      public ITests Template;
  
      public string texter;
  
      public Form1()
      {
          InitializeComponent();
          texter = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) + "\\bin\\dll";
          textBox1.Text = texter;
          string[] array = Directory.GetFiles(texter, "*.dll");
  
          foreach(string file in array)
          {
              textBox1.Text += Environment.NewLine + file;
          }
          Program();
      }
  
      public void Program()
      {
          AggregateCatalog catalog = new AggregateCatalog();
          catalog.Catalogs.Add(new DirectoryCatalog(texter));
          Console.WriteLine(catalog.Catalogs);
          try
          {
              CompositionContainer container = new CompositionContainer(catalog);
              container.ComposeParts(this);
          }
          catch (Exception e)
          {
              Console.WriteLine(e.Message);
          }
      }
  } 
  </code></pre>
  
  <p>this is my public interface:
  I've imported them in both projects, so I already tried to avoid the assemblyreference error</p>
  
  <pre><code>namespace ClassLibrary1
  {
      public interface ITests
      {
          string Result(string result);
      }
  }
  </code></pre>
  
  <p>here is my dll with the export code:</p>
  
  <pre><code>namespace WindowsFormsApplication1
  {
      public class Template 
      {
          //Please write all your tests in this class
          //[TestClass]
          public class Tests
          {
              //example of class
              //[TestMethod]
              public class Example : ITests
              {
                  [Export(typeof(ITests))]
                  public string Result(string res)
                  {
                      string resa = res + " dit is door de test gegaan";
                      return resa;
                  }
              }
  
              //[TestMethod]
              public class ExampleTest2
              {
              }
          }
      }
  }
  </code></pre>
  
  <p>I get this error:</p>
  
  <blockquote>
    <p>A first chance exception of type
    'System.ComponentModel.Composition.Primitives.ComposablePartException'
    occurred in System.ComponentModel.Composition.dll
    'WindowsFormsApplication1.vshost.exe' (Managed (v4.0.30319)): Loaded</p>
    
    <blockquote>
      <p>'C:\Windows\assembly\GAC_MSIL\Microsoft.VisualStudio.DebuggerVisualizers\11.0.0.0__b03f5f7f11d50a3a\Microsoft.VisualStudio.DebuggerVisualizers.dll'
      The composition produced a single composition error. The root cause is
      provided below. Review the CompositionException.Errors property for
      more detailed information.</p>
    </blockquote>
    
    <p>1) The export 'WindowsFormsApplication1.Template+Tests+Example.Result (ContractName="ClassLibrary1.ITests")' is not assignable to type 'ClassLibrary1.ITests'.</p>
    
    <p>Resulting in: Cannot set import
    'WindowsFormsApplication1.Form1.Template
    (ContractName="ClassLibrary1.ITests")' on part
    'WindowsFormsApplication1.Form1'. Element:
    WindowsFormsApplication1.Form1.Template
    (ContractName="ClassLibrary1.ITests") --> 
    WindowsFormsApplication1.Form1</p>
  </blockquote>