How To Test #Controller with Spring Boot 2 and WebFlux - spring-boot

Question

I am currently trying to test a simple post method in a normal Controller which returns a Mono to redirect to a different page or in this case the home page. I have tried all sorts of different aproaches mocking components but I always seem to be returning a null Mono in the test all works normally via form submission.
#Controller
public class AddNewEntryController {
private final EntryService service;
#PostMapping("/add-new-entry")
public Mono<String> addNewEntrySubmit(#ModelAttribute("timeEntry") Entry entry) {
return service.addTimeKeepingEntry(Flux.just(entry)).then(Mono.just("redirect:/"));
}
}
And the Service Class Code
public Mono<Void> addTimeKeepingEntry(Flux<Entry> entry) {
return entry.flatMap(entry -> Mono.when(repository.save(entry).log("Save to DB"))
.log("add entry when")).then().log("done");
}
And Test Code
#RunWith(SpringRunner.class)
#WebFluxTest(controllers = AddNewEntryController.class)
#Import({ThymeleafAutoConfiguration.class})
public class AddNewEntryControllerTest {
#Autowired
WebTestClient webTestClient;
#MockBean
EntryService service;
#Test
public void addNewEntrySubmit() {
MultiValueMap<String, String> formData = new LinkedMultiValueMap<>();
formData.add("month", month);
formData.add("dateOfMonth", Integer.toString(21));
formData.add("startTime", "09:00");
when(service.addEntry(Flux.just(entry1))).thenReturn(Mono.empty());
webTestClient.post().uri("/add-new-entry").body(BodyInserters.fromFormData(formData)).exchange().expectStatus().isSeeOther().expectHeader().valueEquals(HttpHeaders.LOCATION, "/");
Whenever I run the test I am always getting a Null Pointer and after debugging it is pointing to Mono as being Null. Problem is I am not sure which Mono or at which step.
The StackTrace I get is as follows.
java.lang.NullPointerException: null
at com.dbeer.timekeeping.UI.AddNewEntryController.addNewEntrySubmit(AddNewEntryController.java:47) ~[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_181]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_181]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_181]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_181]
at org.springframework.web.reactive.result.method.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:243) ~[spring-webflux-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at org.springframework.web.reactive.result.method.InvocableHandlerMethod.lambda$invoke$0(InvocableHandlerMethod.java:138) ~[spring-webflux-5.0.9.RELEASE.jar:5.0.9.RELEASE]
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:118) [reactor-core-3.1.9.RELEASE.jar:3.1.9.RELEASE]
at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1083) ~[reactor-core-3.1.9.RELEASE.jar:3.1.9.RELEASE]
at reactor.core.publisher.MonoZip$ZipCoordinator.signal(MonoZip.java:247) ~[reactor-core-3.1.9.RELEASE.jar:3.1.9.RELEASE]
at reactor.core.publisher.MonoZip$ZipInner.onNext(MonoZip.java:329) ~[reactor-core-3.1.9.RELEASE.jar:3.1.9.RELEASE]
at reactor.core.publisher.FluxPeek$PeekSubscriber.onNext(FluxPeek.java:185) ~[reactor-core-3.1.9.RELEASE.jar:3.1.9.RELEASE]

Answer 1

after looking at your project, the issue seems to be the consistency of naming of controllers and the html page.
e.g. in header.html you had a url to link add-entry but your controller had add-new-entry if you change the url in header to add-new-entry it works.
As a clean up, you should use thmyeleaf to generate the URL not a normal href, as if you ever add security later, thymeleaf will add the session id to the URL etc
***********Edit pulled the branch and could reproduce *******
The line
given(service.addTimeKeepingEntry(Flux.just(new TimeKeepingEntry(month, 21, "Tuesday", "09:00", "30", "17:00", "7.5", false)))).willReturn(Mono.empty());
is the issue, since Mockito matches on Object.equals here and you have not defined what equals means to your object.
another way is to capture the object passed into the mock
e.g.
#Captor
private ArgumentCaptor<Flux<TimeKeepingEntry>> captor;
#Test
public void addNewEntrySubmit() {
MultiValueMap<String, String> formData = new LinkedMultiValueMap<>();
formData.add("month", month);
formData.add("dateOfMonth", Integer.toString(21));
formData.add("day", "Tuesday");
formData.add("startTime", "09:00");
formData.add("endTime", "17:00");
formData.add("breakLength", "30");
given(service.addTimeKeepingEntry(any())).willReturn(Mono.empty());
webTestClient.post().uri("/add-new-entry")
.body(BodyInserters.fromFormData(formData)).exchange().expectStatus().isSeeOther().expectHeader().valueEquals(HttpHeaders.LOCATION, "/");
verify(service).addTimeKeepingEntry(captor.capture());
TimeKeepingEntry timeKeepingEntry = captor.getValue().blockFirst();
assertThat(timeKeepingEntry.getMonth()).isEqualTo(month);
//and whatever else you want to test
}