def test_all_words_many_docs():
    doc1 = {
        'words': ['b', 'c', 'a']
    }
    doc2 = {
        'words': ['b', 'd', 'a']
    }
    doc3 = {
        'words': ['b', 'd', 'e']
    }
    assert_that(all_words([doc1, doc2, doc3])).is_equal_to(
        ['a', 'b', 'c', 'd', 'e'])
def test_all_words_single_doc():
    document = {
        'words': ['b', 'c', 'a']
    }
    assert_that(all_words([document])).is_equal_to(['a', 'b', 'c'])
def test_all_words_empty():
    assert_that(all_words([])).is_equal_to([])