In xUnit/Shouldly/AutoMoq/Autofixture, can we pass in a Type using InlineAutoMoqData that can be used as a in the test itself?

Question

I've got an issue in Unit Testing that I've been unable to solve. I think the most succinct way to say it is:

I want to be able to use a Type provided in a Theory InlineAutoMoqData's parameters as the T in Shouldly's Should.Throw method. This would allow me to create different Row Tests (I guess that's Inline Theories in this framework) expecting varying Exception types, should there be multiple associated with a method.

I am unsure if it's possible, but here is an example of the unit test itself.

[Theory]
[InlineAutoMoqData("bork", typeof(FileTypeNotRecognizedException))]
public void Build_ReturnsSpecificException_FileNamePassedIn(string fileName, Type expected, ProcessFactory sut)
{
    Should.Throw<expected>(() => sut.Build(fileName));
}

The questions I looked at, before getting stumped and posting this, were: Dynamically Create a generic type for template and Creating a Generic<T> type instance with a variable containing the Type

Is something like this possible?

Edit:

I see that in xUnit I can achieve this via the Assert.Throws(Type, Delegate) method.

[Theory]
[InlineAutoMoqData("bork", typeof(FileTypeNotRecognizedException))]
public void Build_ReturnsSpecificException_FileNamePassedIn(string fileName, Type expected, ProcessFactory sut)
{
    Assert.Throws(expected, () => sut.Build(fileName));
}

I would still like to know if there is a way to achieve it whenever I want the Type to be in a Generic Method.

Answer 1

You can't, except using Reflection, similar to the two links you mentioned.

However, you can do a little trick to achieve what you want. This is ugly and impractical and I don't recommend using it, but just for the fun of it...

Create a generic class containing your parameterized test:

public class Test<T> where T : Exception
{
    public virtual void Build_ReturnsSpecificException_FileNamePassedIn(
        string fileName,
        ProcessFactory sut)
    {
        Assert.Throws<T>(() => sut.Build(fileName));
    }
}

For every parameter (Exception type) you create a class inheriting from the generic one, override the test method and use the InlineAutoMoqData:

public class TestFileNotFound : Test<FileTypeNotRecognizedException>
{
    [Theory]
    [InlineAutoMoqData("bork")]
    public override void Build_ReturnsSpecificException_FileNamePassedIn(string fileName,
        ProcessFactory sut)
    {
        base.Build_ReturnsSpecificException_FileNamePassedIn(fileName, sut);
    }
}
public class TestAnotherException : Test<Exception>
{
    [Theory]
    [InlineAutoMoqData("borg")]
    public override void Build_ReturnsSpecificException_FileNamePassedIn(string fileName,
        ProcessFactory sut)
    {
        base.Build_ReturnsSpecificException_FileNamePassedIn(fileName, sut);
    }
}

Of course, you could do the same using a generic method instead of a generic class, but that seems stupid as well:

public void Build_ReturnsSpecificException_FileNamePassedIn<TException>(string fileName,
    ProcessFactory sut)
    where TException : Exception
{
    Assert.Throws<TException>(() => sut.Build(fileName));
}

[Theory]
[InlineAutoMoqData("bork")]
public void Build_ReturnsSpecificException_FileNamePassedIn(string fileName,
    ProcessFactory sut)
{
    Build_ReturnsSpecificException_FileNamePassedIn<FileTypeNotRecognizedException>(fileName, sut);
}

[Theory]
[InlineAutoMoqData("borg")]
public void Build_ReturnsAnotherException_FileNamePassedIn(string fileName,
    ProcessFactory sut)
{
    Build_ReturnsSpecificException_FileNamePassedIn<Exception>(fileName, sut);
}

As you discovered yourself, xUnit.net has a non-generic Assert.Throws that takes a Type and you should use that instead of this hack.