Unit testing and coverage-ing a function using multiprocessing.Process() in python

Question

I am trying to test a function that might crash, using multiprocessing.Process(). The code written below restarts the call if the function doesn't respond ideally within 10 minutes which is working completely fine, even the self.assert... tests are working fine. The problem comes out to be with the coverage, for some reason, running coverage over my files shows that my_func is being called but nothing inside it is getting covered while testing whereas the tests (which require the whole function to be executed without crashing) are passing.

        while True:
           p = multiprocessing.Process(
               target=my_func, args=(return_dict) # return_dict to get the return values
           )
           p.start()
           p.join(600)

           if p.is_alive():
               print(
                   "Taking too long, "
                   + "KILLING IT and starting AGAIN."
               )
               p.kill()
               p.join()
           else:
               break

Is there something that I am doing wrong? Please let me know if the information seems incomplete, I'll add my tests and the function then.

Answer 1

Reference link

For coverage to cover code running in sub-processes you need to actually specify it.

1. Add import coverage import statement in your file

2. Add coverage.process_startup() on top of every multiprocessing.Process() statement, in my case something like this -

   coverage.process_startup()

   p = multiprocessing.Process( target=my_func, args=(return_dict) )

   ....rest of the code

3. Create a .coveragerc file in your root directory and add the following lines to specify covering subprocesses and multiprocessing.

   [run]

   concurrency=multiprocessing

4. Set a path variable called COVERAGE_PROCESS_START to store the location of .coveragerc file

   set COVERAGE_PROCESS_START=%cd%\.coveragerc // Windows

   export COVERAGE_PROCESS_START=$PWD/.coveragerc // UNIX/LINUX

5. You're all set, run the tests using coverage run -m unittest, notice how now there are more than 1 coverage report files generated. To combine them run coverage combine and finally for the report run coverage report