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WebTestClient

WebTestClient is an HTTP client designed for testing server applications. It wraps Spring’s WebClient and uses it to perform requests but exposes a testing facade for verifying responses. WebTestClient can be used to perform end-to-end HTTP tests. It can also be used to test Spring MVC and Spring WebFlux applications without a running server via mock server request and response objects.

Setup

To set up a WebTestClient you need to choose a server setup to bind to. This can be one of several mock server setup choices or a connection to a live server.

Bind to Controller

This setup allows you to test specific controller(s) via mock request and response objects, without a running server.

For WebFlux applications, use the following which loads infrastructure equivalent to the WebFlux Java config, registers the given controller(s), and creates a WebHandler chain to handle requests:

Java
WebTestClient client =
		WebTestClient.bindToController(new TestController()).build();
Kotlin
val client = WebTestClient.bindToController(TestController()).build()

For Spring MVC, use the following which delegates to the {spring-framework-api}/test/web/servlet/setup/StandaloneMockMvcBuilder.html[StandaloneMockMvcBuilder] to load infrastructure equivalent to the WebMvc Java config, registers the given controller(s), and creates an instance of MockMvc to handle requests:

Java
WebTestClient client =
		MockMvcWebTestClient.bindToController(new TestController()).build();
Kotlin
val client = MockMvcWebTestClient.bindToController(TestController()).build()

Bind to ApplicationContext

This setup allows you to load Spring configuration with Spring MVC or Spring WebFlux infrastructure and controller declarations and use it to handle requests via mock request and response objects, without a running server.

For WebFlux, use the following where the Spring ApplicationContext is passed to {spring-framework-api}/web/server/adapter/WebHttpHandlerBuilder.html#applicationContext-org.springframework.context.ApplicationContext-[WebHttpHandlerBuilder] to create the WebHandler chain to handle requests:

Java
@SpringJUnitConfig(WebConfig.class) // (1)
class MyTests {

	WebTestClient client;

	@BeforeEach
	void setUp(ApplicationContext context) {  // (2)
		client = WebTestClient.bindToApplicationContext(context).build(); // (3)
	}
}

  1. Specify the configuration to load

  2. Inject the configuration

  3. Create the WebTestClient

Kotlin
@SpringJUnitConfig(WebConfig::class) // (1)
class MyTests {

	lateinit var client: WebTestClient

	@BeforeEach
	fun setUp(context: ApplicationContext) { // (2)
		client = WebTestClient.bindToApplicationContext(context).build() // (3)
	}
}

  1. Specify the configuration to load

  2. Inject the configuration

  3. Create the WebTestClient

For Spring MVC, use the following where the Spring ApplicationContext is passed to {spring-framework-api}/test/web/servlet/setup/MockMvcBuilders.html#webAppContextSetup-org.springframework.web.context.WebApplicationContext-[MockMvcBuilders.webAppContextSetup] to create a MockMvc instance to handle requests:

Java
@ExtendWith(SpringExtension.class)
@WebAppConfiguration("classpath:META-INF/web-resources") // (1)
@ContextHierarchy({
	@ContextConfiguration(classes = RootConfig.class),
	@ContextConfiguration(classes = WebConfig.class)
})
class MyTests {

	@Autowired
	WebApplicationContext wac; // (2)

	WebTestClient client;

	@BeforeEach
	void setUp() {
		client = MockMvcWebTestClient.bindToApplicationContext(this.wac).build(); // (3)
	}
}

  1. Specify the configuration to load

  2. Inject the configuration

  3. Create the WebTestClient

Kotlin
@ExtendWith(SpringExtension.class)
@WebAppConfiguration("classpath:META-INF/web-resources") // (1)
@ContextHierarchy({
	@ContextConfiguration(classes = RootConfig.class),
	@ContextConfiguration(classes = WebConfig.class)
})
class MyTests {

	@Autowired
	lateinit var wac: WebApplicationContext; // (2)

	lateinit var client: WebTestClient

	@BeforeEach
	fun setUp() { // (2)
		client = MockMvcWebTestClient.bindToApplicationContext(wac).build() // (3)
	}
}

  1. Specify the configuration to load

  2. Inject the configuration

  3. Create the WebTestClient

Bind to Router Function

This setup allows you to test functional endpoints via mock request and response objects, without a running server.

For WebFlux, use the following which delegates to RouterFunctions.toWebHandler to create a server setup to handle requests:

Java
RouterFunction<?> route = ...
client = WebTestClient.bindToRouterFunction(route).build();
Kotlin
val route: RouterFunction<*> = ...
val client = WebTestClient.bindToRouterFunction(route).build()

For Spring MVC there are currently no options to test WebMvc functional endpoints.

Bind to Server

This setup connects to a running server to perform full, end-to-end HTTP tests:

Java
client = WebTestClient.bindToServer().baseUrl("http://localhost:8080").build();
Kotlin
client = WebTestClient.bindToServer().baseUrl("http://localhost:8080").build()

Client Config

In addition to the server setup options described earlier, you can also configure client options, including base URL, default headers, client filters, and others. These options are readily available following bindToServer(). For all other configuration options, you need to use configureClient() to transition from server to client configuration, as follows:

Java
client = WebTestClient.bindToController(new TestController())
		.configureClient()
		.baseUrl("/test")
		.build();
Kotlin
client = WebTestClient.bindToController(TestController())
		.configureClient()
		.baseUrl("/test")
		.build()

Writing Tests

WebTestClient provides an API identical to WebClient up to the point of performing a request by using exchange(). See the WebClient documentation for examples on how to prepare a request with any content including form data, multipart data, and more.

After the call to exchange(), WebTestClient diverges from the WebClient and instead continues with a workflow to verify responses.

To assert the response status and headers, use the following:

Java
client.get().uri("/persons/1")
	.accept(MediaType.APPLICATION_JSON)
	.exchange()
	.expectStatus().isOk()
	.expectHeader().contentType(MediaType.APPLICATION_JSON);
Kotlin
client.get().uri("/persons/1")
	.accept(MediaType.APPLICATION_JSON)
	.exchange()
	.expectStatus().isOk()
	.expectHeader().contentType(MediaType.APPLICATION_JSON)

If you would like for all expectations to be asserted even if one of them fails, you can use expectAll(..) instead of multiple chained expect*(..) calls. This feature is similar to the soft assertions support in AssertJ and the assertAll() support in JUnit Jupiter.

Java
client.get().uri("/persons/1")
	.accept(MediaType.APPLICATION_JSON)
	.exchange()
	.expectAll(
		spec -> spec.expectStatus().isOk(),
		spec -> spec.expectHeader().contentType(MediaType.APPLICATION_JSON)
	);

You can then choose to decode the response body through one of the following:

  • expectBody(Class<T>): Decode to single object.

  • expectBodyList(Class<T>): Decode and collect objects to List<T>.

  • expectBody(): Decode to byte[] for JSON Content or an empty body.

And perform assertions on the resulting higher level Object(s):

Java
client.get().uri("/persons")
		.exchange()
		.expectStatus().isOk()
		.expectBodyList(Person.class).hasSize(3).contains(person);
Kotlin
import org.springframework.test.web.reactive.server.expectBodyList

client.get().uri("/persons")
		.exchange()
		.expectStatus().isOk()
		.expectBodyList<Person>().hasSize(3).contains(person)

If the built-in assertions are insufficient, you can consume the object instead and perform any other assertions:

Java
   import org.springframework.test.web.reactive.server.expectBody

client.get().uri("/persons/1")
		.exchange()
		.expectStatus().isOk()
		.expectBody(Person.class)
		.consumeWith(result -> {
			// custom assertions (e.g. AssertJ)...
		});
Kotlin
client.get().uri("/persons/1")
		.exchange()
		.expectStatus().isOk()
		.expectBody<Person>()
		.consumeWith {
			// custom assertions (e.g. AssertJ)...
		}

Or you can exit the workflow and obtain an EntityExchangeResult:

Java
EntityExchangeResult<Person> result = client.get().uri("/persons/1")
		.exchange()
		.expectStatus().isOk()
		.expectBody(Person.class)
		.returnResult();
Kotlin
import org.springframework.test.web.reactive.server.expectBody

val result = client.get().uri("/persons/1")
		.exchange()
		.expectStatus().isOk
		.expectBody<Person>()
		.returnResult()
Tip
 When you need to decode to a target type with generics, look for the overloaded methods that accept {spring-framework-api}/core/ParameterizedTypeReference.html[ParameterizedTypeReference] instead of Class<T>.

No Content

If the response is not expected to have content, you can assert that as follows:

Java
client.post().uri("/persons")
		.body(personMono, Person.class)
		.exchange()
		.expectStatus().isCreated()
		.expectBody().isEmpty();
Kotlin
client.post().uri("/persons")
		.bodyValue(person)
		.exchange()
		.expectStatus().isCreated()
		.expectBody().isEmpty()

If you want to ignore the response content, the following releases the content without any assertions:

Java
client.get().uri("/persons/123")
		.exchange()
		.expectStatus().isNotFound()
		.expectBody(Void.class);
Kotlin
client.get().uri("/persons/123")
		.exchange()
		.expectStatus().isNotFound
		.expectBody<Unit>()

JSON Content

You can use expectBody() without a target type to perform assertions on the raw content rather than through higher level Object(s).

To verify the full JSON content with JSONAssert:

Java
client.get().uri("/persons/1")
		.exchange()
		.expectStatus().isOk()
		.expectBody()
		.json("{\"name\":\"Jane\"}")
Kotlin
client.get().uri("/persons/1")
		.exchange()
		.expectStatus().isOk()
		.expectBody()
		.json("{\"name\":\"Jane\"}")

To verify JSON content with JSONPath:

Java
client.get().uri("/persons")
		.exchange()
		.expectStatus().isOk()
		.expectBody()
		.jsonPath("$[0].name").isEqualTo("Jane")
		.jsonPath("$[1].name").isEqualTo("Jason");
Kotlin
client.get().uri("/persons")
		.exchange()
		.expectStatus().isOk()
		.expectBody()
		.jsonPath("$[0].name").isEqualTo("Jane")
		.jsonPath("$[1].name").isEqualTo("Jason")

Streaming Responses

To test potentially infinite streams such as "text/event-stream" or "application/x-ndjson", start by verifying the response status and headers, and then obtain a FluxExchangeResult:

Java
FluxExchangeResult<MyEvent> result = client.get().uri("/events")
		.accept(TEXT_EVENT_STREAM)
		.exchange()
		.expectStatus().isOk()
		.returnResult(MyEvent.class);
Kotlin
import org.springframework.test.web.reactive.server.returnResult

val result = client.get().uri("/events")
		.accept(TEXT_EVENT_STREAM)
		.exchange()
		.expectStatus().isOk()
		.returnResult<MyEvent>()

Now you’re ready to consume the response stream with StepVerifier from reactor-test:

Java
Flux<Event> eventFlux = result.getResponseBody();

StepVerifier.create(eventFlux)
		.expectNext(person)
		.expectNextCount(4)
		.consumeNextWith(p -> ...)
		.thenCancel()
		.verify();
Kotlin
val eventFlux = result.getResponseBody()

StepVerifier.create(eventFlux)
		.expectNext(person)
		.expectNextCount(4)
		.consumeNextWith { p -> ... }
		.thenCancel()
		.verify()

MockMvc Assertions

WebTestClient is an HTTP client and as such it can only verify what is in the client response including status, headers, and body.

When testing a Spring MVC application with a MockMvc server setup, you have the extra choice to perform further assertions on the server response. To do that start by obtaining an ExchangeResult after asserting the body:

Java
// For a response with a body
EntityExchangeResult<Person> result = client.get().uri("/persons/1")
		.exchange()
		.expectStatus().isOk()
		.expectBody(Person.class)
		.returnResult();

// For a response without a body
EntityExchangeResult<Void> result = client.get().uri("/path")
		.exchange()
		.expectBody().isEmpty();
Kotlin
// For a response with a body
val result = client.get().uri("/persons/1")
		.exchange()
		.expectStatus().isOk()
		.expectBody<Person>()
		.returnResult()

// For a response without a body
val result = client.get().uri("/path")
		.exchange()
		.expectBody().isEmpty()

Then switch to MockMvc server response assertions:

Java
MockMvcWebTestClient.resultActionsFor(result)
		.andExpect(model().attribute("integer", 3))
		.andExpect(model().attribute("string", "a string value"));
Kotlin
MockMvcWebTestClient.resultActionsFor(result)
		.andExpect(model().attribute("integer", 3))
		.andExpect(model().attribute("string", "a string value"));