def METHOD_NAME():
    # Arrange
    df = pd.DataFrame({'foo': ['a', 'b', np.nan, None], 'bar': [None, 'a', 'b', 'a']})
    # Act
    result = PercentOfNulls(aggregation_method="mean").run(df)
    # Assert
    assert_that(result.display, has_length(greater_than(0)))
    assert_that(result.value, has_length(2))
    assert_that(result.value.iloc[0, 0], equal_to(0.5))
    assert_that(result.value.iloc[1, 0], equal_to(0.25))
    assert_that(result.reduce_output(), np.mean(result.value.iloc[:, 0]))