@Streaming(false)
        @Get("/stringFuture")
        public CompletableFuture<String> stringFuture() {
            return UnmodifiableFuture.completedFuture("stringFuture");
        }
A mock service for testing {@link ServerSentEventResponseConverterFunction}.
core/src/test/java/com/linecorp/armeria/internal/server/annotation/ResponseStreamingTest.java