  @Test
  public void should_return_list_of_books_by_author() {


    BookListByAuthorInputData bookListByAuthorInputData = BookListByAuthorInputData.builder()
        .author(ROBERT_C_MARTIN)
        .build();

    Optional<List<Book>> books = Optional.of(Collections.singletonList(cleanArchitectureBook));

    when(bookGateway.findByAuthor(any(String.class))).thenReturn(books);

    List<BookOutputData> bookOutputData =  findBookListsByAuthorInteractor.getBooks(bookListByAuthorInputData);

    assertThat(bookOutputData.size()).isNotZero();
    assertThat(bookOutputData.get(0).getAuthor()).isEqualTo(ROBERT_C_MARTIN);
  }