BAEL-9470: A Guide to RestTestClient

spring-boot-modules/spring-boot-4/pom.xml

@@ -42,6 +42,7 @@
             <groupId>org.projectlombok</groupId>
             <artifactId>lombok</artifactId>
             <optional>true</optional>
+            <scope>provided</scope>
         </dependency>
         <dependency>
             <groupId>org.mapstruct</groupId>
@@ -62,6 +63,10 @@
             <artifactId>spring-boot-starter-test</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-webflux</artifactId>
+        </dependency>
     </dependencies>
 
     <profiles>
@@ -145,6 +150,10 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>21</source> <!-- Or 16+ if Java 21 is too aggressive -->
+                    <target>21</target>
+                </configuration>
             </plugin>
         </plugins>
     </build>

spring-boot-modules/spring-boot-4/src/test/java/com/baeldung/spring/resttestclient/RestTestClientTest.java

@@ -0,0 +1,168 @@
+package com.baeldung.spring.resttestclient;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.List;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.core.ParameterizedTypeReference;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.test.web.servlet.client.RestTestClient;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.context.WebApplicationContext;
+
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+@SpringBootTest
+public class RestTestClientTest {
+
+    @Autowired
+    private MyController myController;
+
+    @Autowired
+    private AnotherController anotherController;
+
+    @Autowired
+    private RestTestClient restTestClient;
+
+    @BeforeEach
+    void beforeEach(WebApplicationContext context) {
+        restTestClient = RestTestClient.bindToController(myController, anotherController)
+            .build();
+    }
+
+    @Test
+    void givenValidPath_WhenCalled_ThenReturnOk() {
+        restTestClient.get()
+            .uri("/persons/1")
+            .accept(MediaType.APPLICATION_JSON)
+            .exchange()
+            .expectStatus()
+            .isOk()
+            .expectBody(Person.class)
+            .isEqualTo(new Person(1L, "John Doe"));
+    }
+
+    @Test
+    void givenWrongCallType_WhenCalled_ThenReturnClientError() {
+        restTestClient.post() // <=== wrong type
+            .uri("/persons/1")
+            .accept(MediaType.APPLICATION_JSON)
+            .exchange()
+            .expectStatus()
+            .is4xxClientError();
+    }
+
+    @Test
+    void givenWrongId_WhenCalled_ThenReturnNoContent() {
+        restTestClient.get()
+            .uri("/persons/0") // <=== wrong id
+            .accept(MediaType.APPLICATION_JSON)
+            .exchange()
+            .expectStatus()
+            .isNoContent();
+    }
+
+    @Test
+    void givenInvalidPath_WhenCalled_ThenReturnNotFound() {
+        restTestClient.get()
+            .uri("/invalid")
+            .accept(MediaType.APPLICATION_JSON)
+            .exchange()
+            .expectStatus()
+            .isNotFound();
+    }
+
+    @Test
+    void givenValidId_whenGetPerson_thenReturnsCorrectFields() {
+        restTestClient.get()
+            .uri("/persons/1")
+            .exchange()
+            .expectStatus()
+            .isOk()
+            .expectBody()
+            .jsonPath("$.id")
+            .isEqualTo(1)
+            .jsonPath("$.name")
+            .isEqualTo("John Doe");
+    }
+
+    @Test
+    void givenValidRequest_whenGetPerson_thenPassesAllAssertions() {
+        restTestClient.get()
+            .uri("/persons/1")
+            .accept(MediaType.APPLICATION_JSON)
+            .exchange()
+            .expectStatus()
+            .isOk()
+            .expectBody(Person.class)
+            .consumeWith(result -> {
+                assertThat(result.getStatus()
+                    .value()).isEqualTo(200);
+                assertThat(result.getResponseBody()
+                    .name()).isEqualTo("John Doe");
+            });
+    }
+
+    @Test
+    void givenValidQuery_whenGetPersonsStream_thenReturnsFlux() {
+        restTestClient.get()
+            .uri("/persons")
+            .accept(MediaType.APPLICATION_JSON)
+            .exchange()
+            .expectStatus()
+            .isOk()
+            .expectBody(new ParameterizedTypeReference<List<Person>>() {});
+    }
+
+    @Test
+    void givenValidQueryToSecondController_whenGetPenguinMono_thenReturnsEmpty() {
+        restTestClient.get()
+            .uri("/pink/penguin")
+            .accept(MediaType.APPLICATION_JSON)
+            .exchange()
+            .expectStatus()
+            .isOk()
+            .expectBody(Penguin.class)
+            .value(it -> assertThat(it).isNull());
+    }
+}
+
+@RestController("my")
+class MyController {
+
+    @GetMapping("/persons/{id}")
+    public ResponseEntity<Person> getPersonById(@PathVariable Long id) {
+        return id == 1 ? ResponseEntity.ok(new Person(1L, "John Doe")) : ResponseEntity.noContent()
+            .build();
+    }
+
+    @GetMapping("/persons")
+    public Flux<Person> getAllPersons() {
+        var persons = List.of(
+            new Person(1L, "John Doe"),
+            new Person(2L, "James Bond"),
+            new Person(3L, "Alice In Wonderland")
+        );
+        return Flux.fromIterable(persons);
+    }
+}
+
+@RestController("my2")
+class AnotherController {
+
+    @GetMapping("/pink/penguin")
+    public Mono<Penguin> getPinkPenguin() {
+        return Mono.empty();
+    }
+}
+
+record Person(Long id, String name) { }
+record Penguin(Long id) { }