Unit test practices in Phobos

[Lars T. Kyllingstad]

I just filed a bug report (3240) that describes a case where IFTI is 
used in Phobos, and where this causes errors when the function is used 
with a different type than the one used in the unittest. (The well known 
"IFTI doesn't work with implicit conversions" problem.) I have a strong 
suspicion that there are many other cases like this waiting to be 
discovered.

I have encountered such errors in my own code many times, and lately 
I've been trying to get into the habit of writing unittests for all (or 
at least more than one) types. Not full-fledged functionality tests, 
mind you -- something like this is usually sufficient:

   T foo(T)(T x) if (isFloatingPoint!T) { return x + 1.0; }

   unittest
   {
       // Test different types
       alias foo!float foo_float;
       alias foo!double foo_double;
       alias foo!real foo_real;

       // Test functionality
       assert (foo(2.0) == 3.0);
   }

For the cases where any type is allowed (or a lot of them, at least) 
even this can become a time-consuming task. In these cases it should at 
least be possible to make a representative selection of types to check.

I just wanted to recommend this as "good practice" to all, but 
especially to the Phobos authors. In my experience this catches a lot of 
bugs which are otherwise hard to spot.

-Lars