LineBlobClientImpl implements LineBlobClient { @Override public CompletableFuture<MessageContentResponse> getRichMenuImage(final String richMenuId) { return toMessageContentResponseFuture(retrofitImpl.getRichMenuImage(richMenuId)); }  @Override CompletableFuture<MessageContentResponse> getMessageContent(final String messageId); @Override CompletableFuture<MessageContentResponse> getRichMenuImage(final String richMenuId); @Override CompletableFuture<BotApiResponse> setRichMenuImage(
            final String richMenuId, final String contentType, final byte[] content);  }
@Test public void getRichMenuImageTest() throws Exception { whenCall(retrofitMock.getRichMenuImage(any()), ResponseBody.create(MediaType.parse("image/jpeg"), ZERO_BYTES)); final MessageContentResponse messageContentResponse = target.getRichMenuImage("ID").get(); verify(retrofitMock, only()).getRichMenuImage("ID"); assertThat(messageContentResponse.getLength()).isZero(); }