@Test
public void testCreateMessageWithFile() throws IOException {

    MessageCreateRequest req = MessageCreateRequest.builder()
            .content("Hello world with file!")
            .build();
    try (InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream("fileTest.txt")) {
        if (inputStream == null) {
            throw new NullPointerException();
        }
        byte[] bytes = readAllBytes(inputStream);
        MultipartRequest<MessageCreateRequest> request = new MultipartRequest<>(
                req, "fileTest.txt", new ByteArrayInputStream(bytes)
        );
        channelService.createMessage(permanentChannel, request).block();
    }
}