Dynamically assert exception type with xUnit Theory

[sgabler]

I'm trying to find an elegant solution for my current problem, but I'm probably approaching this incorrectly. Maybe one of you has a good idea how to improve this?

Here's my code:

public class OAuthServiceTests
{
    [Theory]
    [MemberData(nameof(InvalidProcessAccessTokenInput))]
    public async Task ProcessAccessTokenInput_should_throw_exception_for_invalid_input(TokenController.AccessTokenInput input, Type expectedException)
    {
        // Arrange
        var oAuthService = new OAuthService(null);
        
        // Act
        Func<Task> act = () => oAuthService.ProcessAccessTokenInput(input, string.Empty, CancellationToken.None);

        // Assert
        await act.Should().ThrowAsync<expectedException>();
    }

    public static TheoryData<TokenController.AccessTokenInput, Type> InvalidProcessAccessTokenInput =>
        new()
        {
            { new TokenController.AccessTokenInput { GrantType = "wrong" }, typeof(UnsupportedGrantTypeException) },
            { new TokenController.AccessTokenInput { }, typeof(InvalidInputException) }
        };
}

Of course this doesn't compile. I didn't find a method in FluentAssertions that I could use instead.

But I hope from the example it's clear what I want to achieve. In short: I want to pass the expected exception type in the Theory, and then do the assertion with FluentAssertions.

I searched, but it seems that this is not expected/recommended behavior. Do I have to write a switch statement for each exception type instead?

[jnyrup]

You're so close!

In our test suite we use have this test using a generic test and non-generic memberdata.

fluentassertions/Tests/FluentAssertions.Specs/Exceptions/ExceptionAssertionSpecs.cs

Lines 31 to 38 in 17c52d0

	[Theory]
	[MemberData(nameof(AggregateExceptionTestData))]
	public void When_the_expected_exception_is_wrapped_it_should_succeed<T>(Action action, T _)
	where T : Exception
	{
	// Act/Assert
	action.Should().Throw<T>();
	}

I just checked and you should be able to use

[Theory]
[MemberData(nameof(InvalidProcessAccessTokenInput))]
public async Task ProcessAccessTokenInput_should_throw_exception_for_invalid_input<T>(TokenController.AccessTokenInput input, T _)
    where T : Exception
{
    // Arrange
    var oAuthService = new OAuthService(null);
    
    // Act
    Func<Task> act = () => oAuthService.ProcessAccessTokenInput(input, string.Empty, CancellationToken.None);

    // Assert
    await act.Should().ThrowAsync<T>();
}

public static TheoryData<TokenController.AccessTokenInput, Exception> InvalidProcessAccessTokenInput => new()
{
    { new TokenController.AccessTokenInput { GrantType = "wrong" }, new UnsupportedGrantTypeException() },
    { new TokenController.AccessTokenInput { }, new InvalidInputException() }
};

[sgabler]

Thanks, that works perfectly! No ugly switch statement anymore 👍