Python Cookbook 2Nd Edition Jun 1002005 [Electronic resources] نسخه متنی

Recipe 8.9. Running Unit Tests Automatically

Credit: Justin Shaw

Problem

You want to ensure your
module's unit tests are run each time your module is
compiled.

Solution

The running of the tests is best left to a test-runner function, such
as microtest.test shown previously in Recipe 8.8. To make it automatic, save
the following code in a module file pretest.py
somewhere on your Python sys.path. (If you are
using a test-runner function other than
microtest.test, change the import statement and the
runner=microtest.test default value.)

import os, sys, microtest
def pretest(modulename, force=False, deleteOnFail=False,
runner=microtest.test, verbose=False, log=sys.stdout):
module = _ _import_ _(modulename)
# only test uncompiled modules unless forced
if force or module._ _file_ _.endswith('.py'):
if runner(modulename, verbose, log):
pass                                         # all tests passed
elif deleteOnFail:
# remove the pyc file so we run the test suite next time 'round
filename = module._ _file_ _
if filename.endswith('.py'):
filename = filename + 'c'
try: os.remove(filename)
except OSError: pass

Now, you just have to include in each of your
modules' bodies the code:

import pretest
if _ _name_ _ != '_ _main_ _':   
 # when module imported, NOT run as main script
pretest.pretest(_ _name_ _)

Discussion

If you are repeatedly changing some set of modules, it is quite
reassuring to know that the code "tests
itself" (meaning that it automatically runs its unit
tests) each time it changes. (Each time it changes is the same as
each time the module gets recompiled. Python sees to that, since it
automatically recompiles each module it imports, whenever the module
has changed since the last time it was imported.) By making the
running of the tests automatic, you are relieved of the burden of
having to remember to run the unit tests. Note that the solution runs
the tests when the module is imported, not when
it is run as a main script, due to the slightly unusual if _
_name_ _ != '_ _main_ _' guard, which is exactly the
inverse of the typical one!

Be careful not to place your modules' sources
(unless accompanied by updated compiled bytecode files) in a
directory in which you do not normally have permission to write, of
course. It is a bad idea in any case, since Python, unable to save
the compiled .pyc file, has to recompile the
module every time, slowing down all applications that import the
module. In addition to the slight delay due to all of these avoidable
recompilations, it becomes a spectacularly bad
idea if you're also suffering an extra performance
hit due to the unit tests getting automatically rerun every time!
Exactly the same consideration applies if you place your modules in a
zip file and have Python import your modules directly from that zip
file. Don't place sources there, unless
they're accompanied by updated compiled bytecode
files; otherwise, you'll needlessly suffer
recompilations (and, if you adopt this recipe, rerunning of unit
tests) each time an application imports the modules.

See Also

Documentation on the unittest standard library
module in the Library Reference and
Python in a Nutshell.