XUnit and AutoFixture

Question

Is it possible to configure AutoFixture so that for a certain property (e.g. Name) a value is chosen from a list?

F.e.

public class Person
{
   public string FirstName { get; set; }
}

In my test:

[Theory, AutoData]
public void Test(Person person)
{
   // person.FirstName can only be one of these names: "Marc, Jules, Tom"
}

I want to limit the possible values of a string property, is this possible? It's comparable to the Bogus PickRandom()...

Maybe by inheriting from the AutoDataAttribute?

Answer 1

Yep. There is a similar feature implemented in AutoFixture to generate domain names.

You can find the adopted version of the DomainNameGenerator which selects person names from the predefined list:

public class PersonNameGenerator : ISpecimenBuilder
{
    private readonly ElementsBuilder<string> _nameBuilder = 
        new ElementsBuilder<string>("Marc", "Jules", "Tom");

    public object Create(object request, ISpecimenContext context)
    {
        if (context == null) throw new ArgumentNullException(nameof(context));

        if (request == null || !typeof(Person).Equals(request))
            return new NoSpecimen();

        var firstName = this._nameBuilder.Create(typeof(string), context) as string;
        if (firstName == null)
            return new NoSpecimen();

        return new Person { FirstName = firstName };
    }
}

Now the new generator needs to be registered:

public class MyAutoDataAttribute : AutoDataAttribute
{
    public MyAutoDataAttribute()
        : base(() =>
        {
            var fixture = new Fixture();
            fixture.Customizations.Insert(0, new PersonNameGenerator());
            return fixture;
        })
    {
    }
}

The name generator in action:

[Theory, MyAutoData]
public void Test(Person person)
{
    Console.Out.WriteLine("person.FirstName = {0}", person.FirstName);
    // writes:
    // person.FirstName = Tom
    // person.FirstName = Jules
    // person.FirstName = Marc
}

Please note that this implementation will not generate other props (e.g. LastName) if any. More advanced version might be needed but this one is ok to get started.