Frequently asked questions

Q: I use nose to run my tests, and its cover plugin doesn’t let me create HTML or XML reports. What should I do?

First run your tests and collect coverage data with nose and its plugin. This will write coverage data into a .coverage file. Then run coverage.py from the command line to create the reports you need from that data.

Q: Why do unexecutable lines show up as executed?

Usually this is because you’ve updated your code and run coverage on it again without erasing the old data. Coverage records line numbers executed, so the old data may have recorded a line number which has since moved, causing coverage to claim a line has been executed which cannot be.

If you are using the -x command line action, it doesn’t erase first by default. Switch to the coverage run command, or use the -e switch to erase all data before starting the next run.

Q: Why do the bodies of functions (or classes) show as executed, but the def lines do not?

This happens because coverage is started after the functions are defined. The definition lines are executed without coverage measurement, then coverage is started, then the function is called. This means the body is measured, but the definition of the function itself is not.

To fix this, start coverage earlier. If you use the command line to run your program with coverage, then your entire program will be monitored. If you are using the API, you need to call coverage.start() before importing the modules that define your functions.

Q: Does coverage.py work on Python 3.x?

Yes, Python 3 is fully supported.

Q: Isn’t coverage testing the best thing ever?

It’s good, but it isn’t perfect.

Q: Where can I get more help with coverage.py?

You can discuss coverage.py or get help using it on the Testing In Python mailing list.

Bug reports are gladly accepted at the Bitbucket issue tracker.

Announcements of new coverage.py releases are sent to the coveragepy-announce mailing list.

I can be reached in a number of ways, I’m happy to answer questions about using coverage.py.

History

Coverage.py was originally written by Gareth Rees. Since 2004, Ned Batchelder has extended and maintained it with the help of many others. The change history has all the details.

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