FAQ and other help¶
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.py on it again without erasing the old data. Coverage.py records line numbers executed, so the old data may have recorded a line number which has since moved, causing coverage.py 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.py is started after the functions are defined. The definition lines are executed without coverage measurement, then coverage.py 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.py earlier. If you use the command line to run your program with coverage.py, 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: Coverage.py is much slower than I remember, what’s going on?
Make sure you are using the C trace function. Coverage.py provides two
implementations of the trace function. The C implementation runs much faster.
To see what you are running, use
coverage debug sys. The output contains
details of the environment, including a line that says either
tracer: CTracer or
tracer: PyTracer. If it says
PyTracer then you
are using the slow Python implementation.
Try re-installing coverage.py to see what happened and if you get the CTracer as you should.
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.