std.unittests for (final?) review

[Jonathan M Davis]

Okay. As some of you are aware, I created a module with unit testing functions 
when I wrote std.datetime, and it really helped with writing the unit tests for 
std.datetime. It has been at least somewhat reviewed here previously, and that 
has definitely improved it. However, it has not yet been decided whether it's 
going to go into Phobos along with std.datetime. I'd like it to, but it hasn't 
been voted on, and I'm not sure that it's been reviewed as heavily as it should 
be. So, I'm posting the most up-to-date version in the hopes of getting any 
necessary changes found and made so that it can be voted on. Andrei has yet to 
weigh in on std.unittests at all, so I don't know if we're actually going to get 
a vote on it, but I'm presenting it for (final?) review so that it can be voted 
in if that's what he wants to do.

The code: http://is.gd/jZEVl


Both the source file and the ddoc hmtl file are included. And unlike std.datetime, 
it's actually straightforward enough that it makes sense for your average 
program to actually look at it.

To be clear, this module has 2 purposes:

1. Improve error messages on test failure. A good example of this is 
assertEqual, which prints out both of the values being compared so that you 
don't have to add a print statement (or run a debugger) and rerun the test to 
see what the actual values were.

2. Reduce boiler-plate code in unit tests. A good example of this is 
assertExThrown. Testing whether a function call actually throws an exception 
like it's supposed to becomes a single line of code instead of being around 10 
lines.

This module does _not_ attempt to change how unit testing in D fundamentally 
works. It does not print out on success. It doesn't make it so that a unittest 
block continues after a failure occurs in that block. All of the assertXXX 
functions throw an AssertError upon failure - just like assert does, but the 
message in the AssertError is far more informative. While improvements can be 
made to how unit tests work in D, I believe that that should be addressed by 
actually making those improvements to the core language as opposed to using a 
module in Phobos to change things. You shouldn't _need_ std.unittests to write 
unit testing code.

std.unittests is intended to help you write more informative unit test code and 
save you from writing some of the boilerplate code in unit tests, but it is 
_not_ intended to fundamentally alter how unit tests in D function.

So, please have a look at the code. I've made changes according to previous 
suggestions, and I think that the result is quite a bit better than my original 
proposal. If all goes well, perhaps Andrei will put it up for vote soon, and we 
can actually have it in Phobos.

- Jonathan M Davis