title: coverage in parallel for django tests
body: <p>I am running the following through a <code>Makefile</code>:</p>
  <pre><code>NPROCS:=$(shell /usr/bin/nproc)
  
  .PHONY: coverage-app
  coverage-app:
      coverage erase --rcfile=./.coveragerc-app
      coverage run --parallel-mode --rcfile=./.coveragerc-app manage.py test -v 3 --parallel=$(NPROCS) app
      coverage combine --rcfile=./.coveragerc-app
      coverage report -m --rcfile=./.coveragerc-app
  </code></pre>
  <p>If I set <code>NPROCS</code> to 1, I get the expected 100% test coverage of all files within <code>app</code>. However, if <code>NPROCS</code> is greater than 1, I get lots of missing lines in my report.</p>
  <p>What am I doing wrong?</p>
  <p>My <code>.coveragerc-app</code> is as follows:</p>
  <pre><code># Control coverage.py
  [run]
  branch = True
  omit = */__init__*
         */test*.py
         */migrations/*
         */urls.py
         app/admin.py
         app/apps.py
  source = app
  parallel = true
  
  [report]
  precision = 1
  show_missing = True
  ignore_errors = True
  exclude_lines =
      pragma: no cover
      raise NotImplementedError
      except ImportError
      def __repr__
      if self\.logger\.debug
      if __name__ == .__main__.:
  </code></pre>