code: def coverage(c, html=True):
      
      # NOTE: this MUST use coverage itself, and not pytest-cov, because the
      # latter is apparently unable to prevent pytest plugins from being loaded
      # before pytest-cov itself is able to start up coverage.py! The result is
      # that coverage _always_ skips over all module level code, i.e. constants,
      # 'def' lines, etc. Running coverage as the "outer" layer avoids this
      # problem, thus no need for pytest-cov.
      # NOTE: this does NOT hold true for NON-PYTEST code, so
      # pytest-relaxed-USING modules can happily use pytest-cov.
      c.run("coverage run --source=pytest_relaxed -m pytest")
      if html:
          c.run("coverage html")
          c.run("open htmlcov/index.html")
docs: Run coverage with coverage.py.