code: def unit(session, py):
      
  
      # Run unit tests against all supported versions of Python.
      session.interpreter = 'python{}'.format(py)
  
      # Install all test dependencies.
      session.install('-r', 'requirements-test.txt')
  
      # Install dev packages.
      _install_dev_packages(session)
  
      # Run py.test against the unit tests.
      session.run(
          'py.test',
          '--quiet',
          '--cov=opencensus',
          '--cov=context',
          '--cov=contrib',
          '--cov-append',
          '--cov-config=.coveragerc',
          '--cov-report=',
          '--cov-fail-under=97',
          'tests/unit/',
          'context/',
          'contrib/',
          *session.posargs
      )
docs: Run the unit test suite.