ANN: pry unit testing framework

[Aldo Cortesi]

Thus spake Roy Smith (roy at panix.com):

> I've been following this thread for a while with a mix of amusement and 
> alarm.  Contributing code to the community is a good thing, and should be 
> celebrated.  If people like it, they will use it.  If they don't, it will 
> be ignored.  None of which justifies the hostility this thread seems to 
> have degenerated into.

I agree entirely - I've been astonished by the whole fracas myself. I'm
offering Pry simply as something neat I wrote that other people might
find useful, no more.

> In any case, I don't understand why you say that unittest doesn't use
> "assertion-based testing".  They seem like assertions to me.  What am
> I missing?

While you can use the built-in "assert" statement in unittest tests, it
turns out to be annoying in practice, especially during rapid
code-test-code iterations. The problem is that assert traceback errors
are uninformative - when "assert a == b()" fails, there's no way to
tell what a and b() were in this context. Unittest copes with this with
convenience methods - instead you write self.assertEqual(a, b()), which
then gives you proper error reporting.

I think it was py.test that first introduced some magic that picks up
the AssertionError traceback, parses the original expression, and then
re-evaluates its components to give you an error featuring the
"disassembled" assertion expression.  This approach has been adopted by
nose and independently by pry.  While re-evaluation has some
limitations (like not dealing well with expressions that change state),
using assertions makes for more fluid and natural expression in tests.
Maybe "assertion-based" is not an exact phrase to describe this -
saying that these frameworks support "expanded error reporting for
Python assert statements" might be more accurate.



Regards,




Aldo


-- 
Aldo Cortesi
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