Asserting Async Methods Throw Exceptions with FluentAssertions

Harry Bellamy

- One minute read - 98 words

I always forget the syntax when verifying that async methods throw a particular exception with FluentAssertions. This post is to help me (and hopefully others) quickly find the solution to this slightly un-intuitive syntax.

Below is an outline of a test that would perform this verification with FluentAssertions and xUnit.

using FluentAssertions;
using System;
using System.Threading.Tasks;
using xUnit;

public class MyTestClass
{
    [Fact]
    public async Task AsyncExceptionTest()
    {
        var service = new MyService();

        Func<Task> act = async () => { await service.MethodThatThrows(); };
        await act.Should().ThrowAsync<InvalidOperationException>();
    }
}

You can find out more about asserting exceptions with FluentAssertions here.