How to combine a Convention-based Customization with AutoFixture's [AutoData] attribute?

Question

I am using AutoFixture's [AutoData] attribute to provide some unit tests (NUnit) with an instance of a POCO. For example:

[Test, AutoData]
public void Create_NameIsNull_ThrowsException(MyPOCO myPOCO) {..}

I've recently added a new string property to my POCO that must always contain a properly formed URL.

Naturally, [AutoData] is not aware of this requirement and generates the usual GUID-based string value for this property. This causes my tests to fail (because of some Data Annotations based validation that I have in place).

I've followed @ploeh's advice and written a Convention-based Customization for AutoFixture that specifically generates a properly formatted URL string for this new property of mine. It is a class called UrlSpecimenBuilder that implements ISpecimenProvider.

My question is, how can I combine my new ISpecimenProvider with [AutoData]?

I don't want to have to go fixture.Customizations.Add(new UrlSpecimenBuilder()); in each one of my unit test. I'm looking for a single test fixture setup step that will do the same thing.

Answer 1

You should define your own version of the AutoDataAttribute and apply all the customizations you need. If the customizations are relevant for all the tests, it might be called DefaultAutoData:

[Test, DefaultAutoData]
public void Create_NameIsNull_ThrowsException(MyPOCO myPOCO) {..}

internal class DefaultAutoDataAttribute : AutoDataAttribute
{
  public DefaultAutoDataAttribute()
    : base(new Fixture().Customizations.Add(new UrlSpecimenBuilder()))
  {
  }
}

See this Mark Seemann post for details.

Answer 2

You can also override the CustomizeAttribute to arrive at a syntax like

[Test, AutoData]
public void Create_NameIsNull_ThrowsException(
  [MyPOCOWithValidUrl] MyPOCO myPOCO) 
{..}

Some real world examples