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    Assert.ThrowsAsync

    The Assert.ThrowsAsync is the async equivalent to Assert.Throws for asynchronous code. See Assert.Throws for more information.

    Exception Assert.ThrowsAsync(Type expectedExceptionType, AsyncTestDelegate code);
    Exception Assert.ThrowsAsync(Type expectedExceptionType, AsyncTestDelegate code,
                                 string message, params object[] params);
    
    Exception Assert.ThrowsAsync(IResolveConstraint constraint, AsyncTestDelegate code);
    Exception Assert.ThrowsAsync(IResolveConstraint constraint, AsyncTestDelegate code,
                                 string message, params object[] params);
    
    TActual Assert.ThrowsAsync<TActual>(AsyncTestDelegate code);
    TActual Assert.ThrowsAsync<TActual>(AsyncTestDelegate code,
                                        string message, params object[] params);
    

    In the above code AsyncTestDelegate is a delegate of the form Task AsyncTestDelegate(), which is used to execute the code in question. This will likely be a lambda expression.

    The following example shows the most common way of writing tests.

    [TestFixture]
    public class AssertThrowsTests
    {
      [Test]
      public void Tests()
      {  
        // Using a method as a delegate
        Assert.ThrowsAsync<ArgumentException>(async () => await MethodThatThrows());
      }
      
      async Task MethodThatThrows()
      {
        await Task.Delay(100);
        throw new ArgumentException();
      }
    }
    

    This example shows use of the return value to perform additional verification of the exception. Note that you do not need to await the result.

    [TestFixture]
    public class UsingReturnValue
    {
      [Test]
      public async Task TestException()
      {
        MyException ex = Assert.ThrowsAsync<MyException>(async () => await MethodThatThrows());
    
        Assert.That(ex.Message, Is.EqualTo("message"));
        Assert.That(ex.MyParam, Is.EqualTo(42));
      }
    }
    

    See Also

    • Assert.Catch
    • Assert.CatchAsync
    • Assert.Throws
    • ThrowsConstraint
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