Just an idea that can parhaps be added to phobos or the language itself for unit tests.

Often you want a function to keep it's behavior, or at least be informed when it changed from last time.

I suggest a term test, that when called for the first time, creates a file (using the test name, .tst) and stores the given value.  On the second call of the unittest, the tests would only check if the output had changed. If it had, the tests would write a .bad file and report the inconstancy.  If the user wanted the function to change, they could simply delete the .tst file.  Test would support the basic primitive types (bool, char [], int, float, ect...).

ie //testIt.d

char [] func() {    return "I shouldn't change"; }
char [] func2() {   return "I shouldn't change either"; }

unittest
{
   beginTest("func and func2"); //Starts the testing
   test(func()); //Writes "I shouldn't change." the first time, the second time it checks to make sure that func returns "I shouldn't change."
   test(func2()); //Writes "I shouldn't change either" the first time, the second time it checks to make sure that func returns "I shouldn't change either"
}

unittest
{
   beginTest("func"); //Starts the testing
   test(func()); //Writes "I shouldn't change." the first time, the second time it checks to make sure that func returns "I shouldn't change."
}

The first time it would produce a test file (testIt.tst) like (although it would probably be binary):

func and func2:
I shouldn't change.
I shouldn't change either

func:
I shouldn't change.

The second time, it would just check to make sure it was the same output. If not it would write a testIt.bad file that looks much like the testIt.tst file, but with the inconsistencies.

-Anderson