How to use the sister.MeanEmbedding function in sister

def setUp(self):
        embedding_patcher = patch('sister.word_embedders.FasttextEmbedding')
        embedding = embedding_patcher.start()(lang='en')
        embedding.get_word_vector.return_value = np.random.rand(300)
        embedding.get_word_vectors.side_effect = lambda words: np.random.rand(len(words), 300)

        self.sentence_embedding = MeanEmbedding(
            tokenizer=SimpleTokenizer(),
            word_embedder=embedding
        )
        self.addCleanup(embedding_patcher.stop)