@Streaming(true)
        @Get("/fileMono")
        public Mono<HttpFile> fileMono() {
            return Mono.just(HttpFile.of(HttpData.ofUtf8("fileMono")));
        }
A mock service for testing {@link HttpFileResponseConverterFunction}.
core/src/test/java/com/linecorp/armeria/internal/server/annotation/ResponseStreamingTest.java