BDD and Parameterized testing

Although I really like Astels style BDD still use a lot of parameterized testing and though I should give you an example why, using XUnit.net.

Lets say we’re testing simple SPECIFICATION style rules, in BDD we might write:

[Concerning(typeof(ValidEmailRule<TestEntity>))]
public class When_using_rule_on_a_null_string : SpecificationBase
{
    protected TestEntity _testEntity;
    private bool _isSatisfied;

    protected override void EstablishContext()
    {
        _testEntity = ContextSetup.CreateTestEntityWithValue(null);
    }

    protected override void Act()
    {
        _isSatisfied = new ValidEmailRule<TestEntity>(_testEntity, x => x.Value).IsSatisfied();
    }

    [Observation]
    public void is_satisfied()
    {
        _isSatisfied.ShouldBeTrue();
    }
}

This just tests how the rule handles a null value, but we’d then want to test with all sorts of other values (valid and invalid). To compare lets thus look at how easy it is to test a variety of invalid e-mail address using one of XUnit.net‘s parameterized testing approaches (see Ben Hall for more options):

[Concerning(typeof(ValidEmailRule<TestEntity>))]
public class When_evaluating_invalid_email_addresses
{
    [Theory]
    [InlineData("sddas.com")]
    [InlineData("sddas@")]
    [InlineData("@")]
    [InlineData("@blah.com")]
    [InlineData("sddas@@blah.com")]
    [InlineData("1213231")]
    public void is_not_satisfied(string invalidEmailAddress)
    {
        var testEntity = ContextSetup.CreateTestEntityWithValue(invalidEmailAddress);

        var isSatisfied = new ValidEmailRule<TestEntity>(testEntity, x => x.Value).IsSatisfied();

        isSatisfied.ShouldBeFalse();
    }
}

Now you may disagree with my approach here, this isn’t as readable as it could be, but I think you can see why you’d use this approach if you have a lot of values to validate.