def coveragerc(request, testdir):
    """
    Generates .coveragerc to be used to combine test results from different subprocesses.
    """
    data_file = '%s/.coverage.%s' % (request.config.rootdir, request.node.name)
    return testdir.makefile('.ini', coveragerc='''
    [run]
    branch = true
    data_file = %s

    [report]
    show_missing = true
    precision = 2
    exclude_lines = raise NotImplementedError
    ''' % data_file)