Spring Integration Unit Test

@RunWith(SpringRunner.class)
@SpringBootTest(classes = Application.class)
@SpringIntegrationTest
@ActiveProfiles("local")
@AutoConfigureMockMvc
@TestPropertySource(properties = {
        "my.setting=watchamacallit"
})

public class ApplicationTest {

    @Autowired
    private MockIntegrationContext mockIntegrationContext;

    @Autowired
    private MockMvc mockMvc;

    @Autowired
    private GatewayApplication.ConversionMessagingGateway conversionMessagingGateway;

    @Autowired
    private MyService myService;


    @TestConfiguration
    public static class Configuration {

        @MockBean
        private MyService myService; // injected in SUT and test

    }

    @Test
    public void someRestFlow() throws Exception {
        
        Bar response = new Bar();
        
        mockIntegrationContext.substituteMessageHandlerFor(
           "fooBean",
           MockIntegration.mockMessageHandler()
               .handleNextAndReply(message -> response));
       
       when(myService.foo()).thenReturn(...);
               
        
        mockMvc.perform(
                MockMvcRequestBuilders.post("/foo")
                        .contentType(MediaType.APPLICATION_JSON).content("{}"))
                .andExpect(MockMvcResultMatchers.status()
                        .isOk());
    }
}

Spring Integration WebFlux based Unit Test

@RunWith(SpringRunner.class)
@SpringBootTest(classes = GatewayApplication.class)
@SpringIntegrationTest
@ActiveProfiles("local")
public class ApplicationTest {

    @Autowired
    private ApplicationContext wac;

    @Autowired
    private MockIntegrationContext mockIntegrationContext;

    private WebTestClient webTestClient;

    @Autowired
    private GatewayApplication.ConversionMessagingGateway conversionMessagingGateway;

    @Before
    public void setup() {

        this.webTestClient =
                WebTestClient.bindToApplicationContext(this.wac)
                        //.apply(SecurityMockServerConfigurers.springSecurity())
                        .configureClient()
                        .build();
    }


    @Test
    public void someRestFlow() throws Exception {

        ConversionRequestBuilder response = ConversionRequestBuilder.aConversionRequest();
        
        // currently not working, see https://jira.spring.io/browse/INT-4537 - inject mocked Pojo handler instead as workaround
        mockIntegrationContext.substituteMessageHandlerFor(
                "conversionFlow.org.springframework.integration.config.ConsumerEndpointFactoryBean#1",
                MockIntegration.mockMessageHandler()
                        .handleNextAndReply(message -> response.withFileOriginal(
                                new File("document-with-"
                                        + ((ConversionRequest) message.getPayload()).getDimagID()
                                        + ".docx"))));

        FluxExchangeResult<Object> documentIds = webTestClient.post()
                .uri("/foo")
                .contentType(MediaType.APPLICATION_JSON)
                .syncBody("{}")
                .exchange()
                .expectStatus()
                .isOk()