I'm somewhat new to Unity and dependency injection. I'm trying to write a unit test that goes something like this:

[Test]
public void Test()
{
    UnityContainer container = new UnityContainer();
    DynamicMock myMock = new DynamicMock(typeof(IMyInterface));
    container.RegisterInstance(typeof(IMyInterface), myMock.MockInstance);  //Error here

    // Continue unit test...
}

When this test executes, the container throws an ArgumentNullException inside the RegisterInstance method with the message Value cannot be null. Parameter name: assignmentValueType.

The top line of the stack trace is at Microsoft.Practices.Unity.Utility.Guard.TypeIsAssignable(Type assignmentTargetType, Type assignmentValueType, String argumentName).

Why can't I register a MockInstance with the UnityContainer, and how do I work around this?