Python doctest: skip a test conditionally

问题:

I know how to skip a doctest using # doctest: +SKIP, but I can't figure out how to skip a test sometimes, based on a runtime condition. For example:

>>> if os.path.isfile("foo"):
...    open("foo").readlines()
... else:
...    pass # doctest: +SKIP
['hello', 'world']

That's the sort of thing I want to do. I would also accept a solution which runs the test, but changes the expected result to an exception with traceback if the condition is not met (i.e. run the test unconditionally but modify the expected result).

回答1:

You can return a special value if you don't want the output to be tested. Let's call _skip this special value:

• if the appropriate flag is set and if the value you got is _skip, then the test is a success no matter what was expected
• otherwise (ie. no flag or a normal return value), perform the test a usual.

You need a custom OutputChecker:

_skip = object()
COND_SKIP = doctest.register_optionflag('COND_SKIP')

class CondSkipChecker(doctest.OutputChecker):
    def check_output(self, want, got, optionflags):
        if optionflags & COND_SKIP and got.strip() == str(_skip):
            return True
        else:
            return super(CondSkipChecker, self).check_output(want, got, optionflags)

Here's a proof of concept (the doctest API is a bit cumbersome: one woukld like to use testmod̀ with a checker argument):

"""
>>> 1 if True else _skip
2
>>> 1 if False else _skip
2
>>> 1 if True else _skip # doctest: +COND_SKIP
2
>>> 1 if False else _skip # doctest: +COND_SKIP
2
"""

import doctest, sys
_skip = object()
COND_SKIP = doctest.register_optionflag('COND_SKIP')

class CondSkipChecker(doctest.OutputChecker):
    def check_output(self, want, got, optionflags):
        if optionflags & COND_SKIP and got.strip() == str(_skip):
            return True
        else:
            return super(CondSkipChecker, self).check_output(want, got, optionflags)

finder = doctest.DocTestFinder()
runner = doctest.DocTestRunner(CondSkipChecker())
m = sys.modules.get('__main__')
for test in finder.find(m, m.__name__):
    runner.run(test)
print(runner.summarize())

Output:

**********************************************************************
File "temp.py", line 2, in __main__
Failed example:
    1 if True else _skip
Expected:
    2
Got:
    1
**********************************************************************
File "temp.py", line 4, in __main__
Failed example:
    1 if False else _skip
Expected:
    2
Got:
    <object object at 0x0033B8A8>
**********************************************************************
File "temp.py", line 6, in __main__
Failed example:
    1 if True else _skip # doctest: +COND_SKIP
Expected:
    2
Got:
    1
**********************************************************************
1 items had failures:
   3 of   4 in __main__
***Test Failed*** 3 failures.
TestResults(failed=3, attempted=4)

The two tests without doctest annotation fail as expected. Note: you can easily add a warning if _skip is used without the COND_SKIP flag.

The third test fails (got 1 vs expected 2), but the fourth is a success (got ̀_skip + COND_SKIP vs anything is okay).