So I have a test like the following:
[Fact]
public void Test1()
{
Assert.ThrowsAsync<ArgumentNullException>(() => MethodThatThrows());
}
private async Task MethodThatThrows()
{
await Task.Delay(100);
throw new NotImplementedException();
}
To my surprise, Test1 passes successfully. To make it fail I have to write like this:
Assert.Throws<ArgumentNullException>(() => MethodThatThrows().Wait());
What is the purpose of ThrowsAsync(), if it does not work in the scenario above?
You're supposed to await the result (see xunit's acceptance tests for examples and alternate forms).
[Fact]
async void Test1()
{
await Assert.ThrowsAsync<ArgumentNullException>(() => MethodThatThrows());
}
In this specific degenerate case, you could just return the Task that Assert.ThrowsAsync yields without using await; but in that case, the key thing is to yield the Task back to the xUnit framework, i.e.
[Fact]
Task Test1() =>
Assert.ThrowsAsync<ArgumentNullException>(MethodThatThrows);
await goes at the front of the line!Just in case anyone wants to separate Act and Assert part, below code can be used:
//Act
Task result() => systemUnderTest.AsyncMethodThatThrows();
//Assert
await Assert.ThrowsAsync<Exception>(result);
