def METHOD_NAME(self):
    datasets = robjects.packages.importr('datasets')
    datasets_data = robjects.packages.data(datasets)
    datasets_names = tuple(datasets_data.names())
    assert isinstance(datasets_data.fetch(datasets_names[0]),
                      robjects.Environment)
    with pytest.raises(KeyError):
        datasets_data.fetch('foo_%s' % datasets_names[0])