@pytest.mark.parametrize('title_eng, title_foreign, expected', [('English', 'Foreign', 'English / Foreign'), ('English', None, 'English'), (None, 'Foreign', 'Foreign')])
def test_build_title(title_eng, title_foreign, expected):
    assert (Book.build_title(title_eng, title_foreign) == expected)
@pytest.mark.parametrize('title_eng, title_foreign, expected', [('English', 'Foreign', 'English / Foreign'), ('English', None, 'English'), (None, 'Foreign', 'Foreign')])
def test_build_title(title_eng, title_foreign, expected):
    assert (Book.build_title(title_eng, title_foreign) == expected)