Re: [boost] How do you test complex transformations?

Subject: Re: [boost] How do you test complex transformations?
From: Jim Bell (Jim_at_[hidden])
Date: 2011-03-21 11:28:38

On 1:59 PM, Vicente Botet wrote:
> Jim Bell wrote:
>> On 1:59 PM, Vicente Botet wrote:
>>> [...]
>>> One technique could be to make the transformation by hand and keep track
>>> of
>>> the input -> output association.
>>> Another technique consist in re-implementing the algorithm and check that
>>> both implementations match.
>>>
>> I more often verify a couple test-cases by hand and encode those, paying
>> special attention to boundary conditions, etc.
>>
>> Some situations are complex enough that they warrant test hooks to
>> verify intermediate results. And, yes, I leave the hooks in. E.g., "if
>> (test) test->VerifyIntermdiateX(y,z);" Make sure the test-hook pointer
>> is 0 for production.
>>
>>
> Hi,
>
> what kind of verification do you use to do?
>
> for example if we had
>
> T complex_transformation(T a)
> {
>   T tmp1 = simpler_transformation_x(a);
>   T tmp2 = simpler_transformation_y(tmp);
>   return tmp;
> }
>
> could you complete the example with the use of your test verifications?
> where do comes test?

You're not using your tmp1 and tmp2 in your example. And if you can come
up with simpler_transformation_<n>(), you can test those in isolation.
The examples that come to my mind require looking at salient states of a
variety of objects, disk files, etc.

But the basic form, adapted to your example, would be...

static T_test_interface *test = 0;

T complex_transformation(T a)
{
  T tmp1 = simpler_transformation_x(a);
  if (test)
      test->verify_post_x_pre_y(tmp1);
  T tmp2 = simpler_transformation_y(tmp1);
  return tmp2;
}

A big +1 on inverting an operation, too, when you can.