Question

Can someone tell me why this unit test that checks for exceptions fails? Obviously my real test is checking other code but I’m using Int32.Parse to show the issue.

[Test]
public void MyTest()
{
    Assert.That(Int32.Parse("abc"), Throws.Exception.TypeOf<FormatException>());
}

The test fails, giving this error. Obviously I’m trying to test for this exception and I think I’m missing something in my syntax.

Error   1   TestCase '.MyTest'
failed: System.FormatException : Input string was not in a correct format.
at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)
at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)
at System.Int32.Parse(String s)

based on the documentation at Throws Constraint (NUnit 2.5)

Answer 1

Try this instead:

Assert.That(() => Int32.Parse("abc"), Throws.Exception.TypeOf<FormatException>());

Basically you need to pass a delegate to Assert.That, just like the documentation in your link states (note that I’ve used a lambda expression here, but it should be the same).