nUnit Assert.That(method,Throws.Exception) not catching exceptions

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)

Also you can do this: `Assert.Throws(() => Int32.Parse("abc"));` — Jaider, Jul 02 '12 at 15:28
I was trying to stick with the Assert.That style for this project. I'm not as attached to it as I once I was though. — Jason More, Jul 03 '12 at 15:20

score 77 · Accepted Answer · answered Mar 25 '10 at 15:07

77

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).

answered Mar 25 '10 at 15:07

Klaus Byskov Pedersen

117,245
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ah I had to make in an anonymous delegate... I see that in the documentation now, it just wasn't super clear. Thanks! – Jason More Mar 25 '10 at 15:12
3

Incase someone runs into the fact that their anonymous function returns void, you'll need to do something like: `Assert.That(new Action(() => VoidReturningMethod("abc")), Throws.Exception.TypeOf());` – Marty Neal Feb 01 '13 at 16:59
Thanks @MartinNeal that helped me on the right path, but for me it complained that it had to be a TestDelegate, so I had to do: `new TestDelegate(() => AddBlockingTaskToBox())` or – Brondahl Apr 19 '16 at 20:42

score 9 · Answer 2 · answered Mar 25 '10 at 15:06

9

What test runner are you using? Not all of them work correctly with the exception assertions.

You may have better luck using [ExpectedException (typeof(FormatException))] or even Assert.Throws<FormatException> (() => Int32.Parse("abc"));

answered Mar 25 '10 at 15:06

ermau

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I was using TDD.net and nUnit gui. Your fix worked, but I want to use the fluent syntax. I gave you a point though for the help! – Jason More Mar 25 '10 at 15:13
1

I know this is an old answer that was right at that moment. But for now and future reference, `ExpectedException` attribute is deprecated on NUnit 3.0: https://github.com/nunit/docs/wiki/Breaking-Changes – ferpega Nov 08 '16 at 17:04

nUnit Assert.That(method,Throws.Exception) not catching exceptions

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