How to combine PropertyData and AutoNSubstituteData attributes in xunit/autofixture?

Question

I am using the [AutoNSubstituteData] attribute, which was posted here:

AutoFixture, xUnit.net, and Auto Mocking

I would like to combine this wit

Answer 1

The [Theory] attribute works by looking for one or more 'data source attributes'; for example

• [InlineData]
• [PropertyData]
• [ClassData]
• etc.

The [AutoData] attribute is just another such attribute, as is your derived [AutoNSubstituteData] attribute.

It's possible to add more than one 'data source attribute' to the same [Theory], as witnessed by the idiomatic use of the [InlineData] attribute:

[Theory]
[InlineData("foo")]
[InlineData("bar")]
[InlineData("baz")]
public void MyTest(string text)

This produces three test cases.

It's also possible to combine [PropertyData] and [AutoData], but it probably doesn't do what you want it to do. This:

[Theory]
[AutoNSubstituteData]
[PropertyData("InvalidInvariant")]
public void MyTest(/* parameters go here */)

will result in 1 + n test cases:

• 1 test case from [AutoNSubstituteData]
• n test cases from the InvalidInvariant property

These two attributes know nothing about each other, so you can't combine them in the sense that they're aware of each other.

However, when you're implementing a property, you can write whatever code you'd like, including using a Fixture instance, so why not just do this?

public static IEnumerable InvalidInvariant
{
    get
    {
        var fixture = new Fixture().Customize(new MyConventions());
        // use fixture to yield values...,
        // using the occasional hard-coded test value
    }
}

Another option is to use derive from the InlineAutoDataAttribute, which would enable you to write your test cases like this:

[Theory]
[MyInlineAutoData("foo")]
[MyInlineAutoData("bar")]
[MyInlineAutoData("baz")]
public void MyTest(string text, string someOtherText, int number, Guid id)

This would cause the first argument (text) to be populated with the constants from the attributes, while the remaining parameters are populated by AutoFixture.

Theoretically, you may also be able to combine the [AutoData] and [PropertyData] attributes using the CompositeDataAttribute, but it may not work the way you'd like.

Finally, you could consider using Exude for true first-class parameterized tests.