[TIP] Unittest Changes

Jonathan Lange jml at mumak.net
Sun Jul 20 16:54:08 PDT 2008

On Mon, Jul 21, 2008 at 7:16 AM, Michael Foord
<fuzzyman at voidspace.org.uk> wrote:
> Unless someone beats me to it I'm intending to work on some improvements
> to unittest after I have finished "IronPython in Action", which
> realistically will be a couple more months.

Hi Michael,

I've already started a project along these lines, temporarily called pyunit3k:

I haven't announced it until now because the name sucks and because
it's test coverage is still rather poor. I would love it if you could
take a look at it and tell me what you think.

The aim is to incorporate improvements to unittest that have stood the
test of time in real projects, rather than to come up with blue-sky

> The biggest way I can think of improving unittest is to add automatic
> test discovery:
>    unittests.discover_tests(path='.', pattern='test*.py', recurse=True)
> This will simply search the path provided (defaulting to the current
> directory) matching test files based on the pattern.

At the risk of laboring a point, twisted.trial does this already —
pinch the code from there (or from nose, I guess). In trial's case,
the tests are already written.

> Another change will be the improvement of failure message for
> assertEquals. When comparing long strings it will show a diff, when
> comparing containers it will show you the members that are different
> (lists, sets, dictionaries).

bzrlib has some code along these lines.

I can't recall if pyunit3k has pinched it.

> Other minor changes - have assertRaises return the exception instance so
> that you can assertions about it, possibly container membership
> assertion methods, nothing spectacular.

pyunit3k has this.

> Any other good ideas about ways that unittest could change that don't
> either grow the API greatly or break backwards compatibility?

The big one is addCleanup (again, implemented & used in pyunit3k,
Twisted and bzrlib). The idea is that it allows you to dynamically
create resources in tests without worry.

Here's an example of usage:

    def makeTemporaryDirectory(self):
        d = tempfile.mkdtemp()
        self.addCleanup(shutil.rmtree, d)
        return d

Here's a rough implementation:

def addCleanup(self, f, *a, **kw):
    self._cleanup_stack.append((f, *a, **kw))

def _runCleanups(self, test_result):
    for f, *a, **kw in self._cleanup_stack:
            f(*a, **kw)
            test_result.addError(self, sys.exc_info())

_runCleanups is *always* called, even if setUp() fails (pyunit doesn't
run tearDown if setUp fails).

Once you start writing tests with this, it's very hard to go back.

Thank you for taking the initiative to work at improving unittest.


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