private static Step<HttpObject> expectAggregatedJson(Object publisherOrStream,
                                                         ResponseHeaders headers,
                                                         HttpHeaders trailers) throws Exception {
        final HttpResponse response =
                function.convertResponse(ctx, headers, publisherOrStream, trailers);
        return StepVerifier.create(response)
                           .expectNext(headers)
                           .assertNext(content -> {
                               assertThatJson(((HttpData) content).toStringUtf8())
                                       .isArray().ofLength(4)
                                       .thatContains("foo")
                                       .thatContains("bar")
                                       .thatContains("baz")
                                       .thatContains("qux");
                           });
    }
{@link HttpData} instances which are expected to be produced by the
{@link JacksonResponseConverterFunction} when the function gets the
{@link #TEST_STRINGS} as input.
core/src/test/java/com/linecorp/armeria/server/annotation/JacksonResponseConverterFunctionTest.java