@Test public void cookies() { MultiValueMap<String, ResponseCookie> newCookies = new LinkedMultiValueMap<>(); newCookies.add("name", ResponseCookie.from("name", "value").build()); Mono<RenderingResponse> result = RenderingResponse.create("foo").cookies(cookies -> cookies.addAll(newCookies)).build(); StepVerifier.create(result) .expectNextMatches(response -> newCookies.equals(response.cookies())) .expectComplete() .verify(); }