This post describes how to solve the problem that model validation will not work for ASP.NET MVC 2 (.NET 4.0), when testing a model that uses DataAnnotations and MetadataType to describe for its validation.

First of all, ModelState.IsValid is always true, since the function that sets it to false for invalid models is never executed during the unit test execution. This will cause your controllers to behave incorrectly during your tests.

Second, any MetadataType bindings are ignored during the test execution. This causes the validation within it to be ignored as well, which in turn will cause the model to be valid although an object is invalid.

My situation

I am currently writing tests for a Create method in one of my controllers. I use NUnit as test framework. I have an Entity Framework 4 Entity Model, in which I have a set of entities, e.g. an Employee entity with FirstName, LastName and Ssn properties.

To enable model validation during a unit test run, I create a partial Employee class in the same namespace as the entity. I then create a MetadataType class, which handles validation for the class.

This approach is fully described in this blog post.

In my EmployeeController class, I then have a Create function, that takes an employee and tries to save it. If ModelState is not valid, the controller will return the Create view and display any errors to the user. If the model is valid, however, I create the employee and return the employee list.

Easy enough, right? However, when I started to write tests for these classes, it turned out that ModelState.IsValid was always true, even if the tests received invalid employees. Turns out that model validation is not triggered by the tests.

Trigger model validation within a test

This blog post describes the model state problem then presents a nice solution to this problem: the CallWithModelValidation Controller extension method.

I added this extension method to my MVC 2 project and used it instead of calling Create. The test code that looked like this:

var result = controller.Create(new Employee());

thus became:

var result = controller.CallWithModelValidation(c => c.Create(new Employee()), new Employee());

This makes my unit tests properly trigger model validation, which means that the test suite can now test that the controller behaves correctly for invalid models.

The only problem with this approach, is that the model validation does not catch any errors within the model, even if the model is invalid. After some testing, I noticed that this does only occur for partial objects that use MetadataType to specify model validation. Turns out that MetadataType is ignored within a test context. Thus, the model is always considered to be valid.

Before we proceed, make sure to note that classes that describe their validation attributes directly are correctly validated. The next part is only relevant when you use MetadataType.

Register MetadataType connections before testing

This page discusses the MetadataType problem and InstallForThisAssembly as a solution.

This method must be placed within the same assembly as the model, in other words not the test project. I place it in a ControllerExtensions class file and call it at the beginning of CallWithModelValidation. This will not work if you move the extension to another project, so make sure to have it in the correct project.

Run it before your tests, and everything should work.

Hope this helps.