Re: Testing for errors

Hi Charlie,


> Hi Christian,
>
>   
>> [...]
>>     
>
> Of course, you could use try/catch but that would expose the implementation
> to the test. As a side note, this doesn't bother most of us - the test is
> supposed to have knowledge of the external implementation of the methods
> it tests and any exception is part of that.
>   

Technically yes. But this is exactly what I don't want.
Tests also serve as documentation. And if I would expose that 
exception-stuff in the tests, people might think that they are free to 
handle it. -- But they aren't. The only way to deal with it is to fix 
the program and rebuild.
Also, it's kind of verbose to write those try-catch-blocks everywhere.

> You could also use an ExpectedException attribute, like this...
>
>   
>> [Test, ExpectedException(typeof(DeveloperError-exception))]
>> void at_errorIfIndexOutOfRange()
>> {
>>     // setUp Vector v with some elements
>>     int   outOfRange = -1;
>>     v.at (outOfRange);
>> }
>>     
>
>   

Ok, less verbose, but still that exception-stuff.

> To wrap the processing in an assert as you outlined, the problem
> is that exception is thrown as soon as the argument is evaluated
> and the IsError method is never called. 

Exactly.

> The way around this is
> to use a delegate, either explicit or anonymous depending on the
> version of .NET you are using.
>   

I thought of delegates, too. But couldn't find a way to implement it 
(I'm on .NET 2.0). Of course, the at()-method is not the only one I need 
to wrap in the IsError()-method. Thus I need some kind of generic 
delegate for that, I guess. Is that even possible in C#? I would need 
variable arguments: 0-n of any type; and also variable return types: 
void or any other type. -- But this is what you refer to as explicit, right?
Never heard of anonymous delegates before. Let me do some digging.... 
Ah, I guess I got the pointer. Do you mean something like this?:

Assert.IsError (delegate() {v.at (outOfRange);});

Hmm, not that bad. Looks kind of ruby-ish to me:)

So the IsError()-method would be declared like this, I guess:

delegate void Callback();
void IsError (Callback toBeTestedForError);

I'll try that later and report if it worked....

Thanks and regards,
  Christian

> IMO, this is a bit involved for the case as described... I'd just
> test for the exception, but it's certainly possible if you really
> want to.
>
> Charlie
>
>
>
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