DataAnnotations and MetadataType fails in unit tests
This post describes how to fix model validation for ASP.NET MVC 2, when testing a model that uses DataAnnotations and MetadataType to describe for its validation.
In this case, ModelState.IsValid is always true by default, since the function that sets it to false for invalid models is never executed by the unit tests.
This will cause controllers to behave incorrectly while testing, since the valid flag will return the same value all the time.
MetadataType bindings are also ignored during test execution. This causes the validation to be ignored as well, which will cause the model to be valid although an object is invalid.
My situation
I’m currently writing tests for a Create controller. I use NUnit and have an Entity Framework 4 Entity Model with entities, e.g. an Employee with FirstName, LastName and Ssn.
To enable model validation in unit tests, I create a partial Employee class within the same namespace as the entity and a MetadataType class that handles validation for the class.
This is described in more detail here.
My EmployeeController has a Create function that takes an employee and tries to save it. If the ModelState is invalid, the controller returns the Create view and displays the error.
However, if the model state valid, the controller instead creates the employee and returns the employee list.
When I started to write tests for these classes, ModelState.IsValid was always true, even if the tests used invalid employees. Turns out that model validation isn’t triggered by tests.
Trigger model validation within a test
To trigger model validation in a test, you can use the CallWithModelValidation Controller extension method. Just rewrite this test code:
var result = controller.Create(new Employee());
to instead look like this:
var result = controller.CallWithModelValidation(c => c.Create(new Employee()), new Employee());
This makes the unit test 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 doesn’t catch errors in the model, even if the model is invalid.
After some testing, I noticed that this only occurs for partial objects that use MetadataType to specify model validation. Turns out that MetadataType is ignored by the unit tests.
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 how InstallForThisAssembly can be used to fix this problem.
This method must be placed within the same assembly as the model. I placed it inside 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.