Returns the coverage object of pytest-cov.

def get_cov(config):
    """Returns the coverage object of pytest-cov."""

    # Check with hasplugin to avoid getplugin exception in older pytest.
    if config.pluginmanager.hasplugin('_cov'):
        plugin = config.pluginmanager.getplugin('_cov')
        if plugin.cov_controller:
            return plugin.cov_controller.cov
    return None