Igor Sobreira

Python coverage threshold

Ned Batchelder committed a new feature to coverage.py 2 days ago, it's a way to verify coverage threshold. Basically a way to fail your tests if the coverage is not enough. For now you need to install from the repository to get the new feature

$ pip install hg+https://bitbucket.org/ned/coveragepy#egg=coverage

This is how to use from the command line:

$ coverage run run_my_tests.py 
... running all tests
$ coverage report --fail-under=100
... display the report
$ echo $?
2

If your coverage is not 100% your exit status will be 2. This will make your CI fail if your coverage is not enough :). You can also verify coverage using the python API, in this case you need to verify the return value from report() function, here is an example:

cov = coverage.coverage(..)
cov.start()
ret = run_all_my_tests()
cov.stop()
if ret == 0:
    covered = cov.report()
    assert covered > 100, "Not enough coverage"
...

I've created a decorator to make this easier:

def ensure_coverage(percentage, **cov_options):
    def decorator(function):
        @wraps(function)
        def wrapper(*args, **kw):
            cov = coverage.coverage(branch=True, **cov_options)
            cov.start()
            ret = function(*args, **kw)
            cov.stop()
            if ret == 0:
                covered = cov.report()
                assert covered >= percentage, \
                    "Not enough coverage: {0:.2f}%. You need at least {1}%".format(covered, percentage)
            return ret
        return wrapper
    return decorator

This is an usage example for this django app I'm working on:

@ensure_coverage(99, source=['filecabinet'], omit=['filecabinet/tests/*'])
def runtests():
    test_runner = get_runner(settings)()
    return test_runner.run_tests(['filecabinet'])

if __name__ == '__main__':
    sys.exit(runtests())

Here are the related commits, if you're interested:

https://bitbucket.org/ned/coveragepy/changeset/7ea709fc4c1190cf0ffe0aba1a49e6fffe683d2f https://bitbucket.org/ned/coveragepy/changeset/90014f4defd336f05851bdfc01c2b5af60a933c9 https://bitbucket.org/ned/coveragepy/changeset/ba7267fe525001dba99ed1c2c9d11f0724ad9950

And the discussion on the issue:

https://bitbucket.org/ned/coveragepy/issue/139/easy-check-for-a-certain-coverage-in-tests

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My name is Igor Sobreira and is my website. I'm a software developer working at Real Geeks. I currently live in Hawaii doing the two things that I like most: windsurfing and writing software.

See more about me and get in touch.