We ran into a weird issue at work today. Take a look at the following code:
public class MyException : Exception { }
[TestFixture]
public class TestFixture
{
[Test]
public void Test()
{
var exception = GetThrownException<MyException>(() => { throw new MyException(); });
Assert.IsNotNull(exception);
}
private T GetThrownException<T>(Action action)
where T : Exception
{
try
{
action();
}
catch (T exception)
{
return exception;
}
return null;
}
}
If you simply run that test, without debugging, it works (both with Testdriven.NET and Resharper). If you run it with a debugger, it fails with the following message:
ExceptionWeirdness.MyException: Exception of type 'ExceptionWeirdness.MyException' was thrown.
Pretty weird huh?
Let's change the code of the GetThrownException method to this:
private T GetThrownException<T>(Action action)
where T : Exception
{
try
{
action();
}
catch (T exception)
{
return exception;
}
catch (Exception e)
{
return (T)e;
}
return null;
}
Now the test works all the time, even with the debugger attached.
Weird huh? At first i wondered if it was somehow NUnit related... but then i tried running this program:
public class MyException : Exception { }
class Program
{
static void Main(string[] args)
{
var exception = GetThrownException<MyException>(() => { throw new MyException(); });
}
private static T GetThrownException<T>(Action action)
where T : Exception
{
try
{
action();
}
catch (T exception)
{
return exception;
}
return null;
}
}
Run it without the debugger, and it works. Run it with the debugger and it fails.
This is using .NET 3.5 SP1.
I don't understand why it behaves like this... it should work all the time right? I am overdue for my weekly brain-fart so i might be missing something really stupid though.
Either way, the first person to explain this behavior gets awarded with the "Davy Brion's Hero Of The Week" title 
Oh, and this was in a clean solution... so there's no duplicate MyException types or anything like that.
Pingback: Exceptional exception handling - KoenV
Pingback: Reflective Perspective - Chris Alcock » The Morning Brew #197
Pingback: Dew Drop - October 9, 2008 | Alvin Ashcraft's Morning Dew