var formElements = new NameValueCollection() { {"FirstName","Bubba"},{"MiddleName",""},{"LastName","Gump"} };         
var fakeController = GetControllerContext(formElements);
var valueProvider = new Mock<IValueProvider>();           

var bindingContext = new ModelBindingContext(fakeController,valueProvider.Object,typeof(Guid),null,null);



private static ControllerContext GetControllerContext(NameValueCollection form) {
    Mock<HttpRequestBase> mockRequest = new Mock<HttpRequestBase>();
    mockRequest.Expect(r => r.Form).Returns(form);

    Mock<HttpContextBase> mockHttpContext = new Mock<HttpContextBase>();
    mockHttpContext.Expect(c => c.Request).Returns(mockRequest.Object);

    return new ControllerContext(mockHttpContext.Object,new RouteData(),new Mock<ControllerBase>().Object);
}

然后我刚刚将bindingContext变量传递给实现IModelBinder接口的对象的BindModel方法。