Spring WebFlux, unit testing Mono and Flux

Question

Interested in reactive programming, I played a bit with the Building a Reactive RESTful Web Service guide. And wanted to move forwrad and add some unit tests.

I tried to test my handler (RouterFunction) with plain Junit/Mockito test. But, because it is reactive, the handler returns a Mono<ServerResponse>. So I had to block() it to test the ServerResponse status but was not able to extract his body to test it. While searching the web for a solution, it seems that all the samples are using the WebTestClient.

My question is:

Given that all samples are using WebTestClient to test a reactive REST service and that it is not easier to (unit) test the body of a ServerResponse. Is it a good practice to unit test a RouterFunction or is it better to always do broader tests with the WebTestClient ?

Thanks a lot.

Answer 1

It seems that the best practice is to use the WebTestClient. However this one can be used without a running server;

The spring-test module includes a WebTestClient that can be used to test WebFlux server endpoints with or without a running server.

-- https://docs.spring.io/spring/docs/5.0.0.BUILD-SNAPSHOT/spring-framework-reference/html/web-reactive.html#web-reactive-tests

Answer 2

It depends on what exactly you want to test, for regular method you should use StepVerifier in favor of consume the output of you test. However router functions are unique, because, usually return a serverResponse that contains your data on body, so in that case its better use webClient or webTestClient.