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WebTestClient

WebTestClient is a thin shell around WebClient, using it to perform requests and exposing a dedicated, fluent API for verifying responses. WebTestClient binds to a WebFlux application by using a mock request and response, or it can test any web server over an HTTP connection.

Tip
 Kotlin users: See this section related to use of the WebTestClient.

Setup

To create a WebTestClient you must choose one of several server setup options. Effectively you’re either configuring the WebFlux application to bind to or using a URL to connect to a running server.

Bind to Controller

The following example shows how to create a server setup to test one @Controller at a time:

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

The preceding example loads the WebFlux Java configuration and registers the given controller. The resulting WebFlux application is tested without an HTTP server by using mock request and response objects. There are more methods on the builder to customize the default WebFlux Java configuration.

Bind to Router Function

The following example shows how to set up a server from a RouterFunction:

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

Internally, the configuration is passed to RouterFunctions.toWebHandler. The resulting WebFlux application is tested without an HTTP server by using mock request and response objects.

Bind to ApplicationContext

The following example shows how to set up a server from the Spring configuration of your application or some subset of it:

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

Internally, the configuration is passed to WebHttpHandlerBuilder to set up the request processing chain. See WebHandler API for more details. The resulting WebFlux application is tested without an HTTP server by using mock request and response objects.

Bind to Server

The following server setup option lets you connect to a running server:

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

Client Builder

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 others, 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(). What follows after exchange() is a chained API workflow to verify responses.

Typically, you start by asserting the response status and headers, as follows:

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)

Then you specify how to decode and consume the response body:

  • 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.

Then you can use built-in assertions for the body. The following example shows one way to do so:

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)

You can also go beyond the built-in assertions and create your own, as the following example shows:

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)...
		}

You can also exit the workflow and get a result, as follows:

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 ParameterizedTypeReference instead of Class<T>.

No Content

If the response has no content (or you do not care if it does) use Void.class, which ensures that resources are released. The following example shows how to do so:

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

Alternatively, if you want to assert there is no response content, you can use code similar to the following:

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()

JSON Content

When you use expectBody(), the response is consumed as a byte[]. This is useful for raw content assertions. For example, you can use JSONAssert to verify JSON content, as follows:

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\"}")

You can also use JSONPath expressions, as follows:

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 infinite streams (for example, "text/event-stream" or "application/x-ndjson"), you need to exit the chained API (by using returnResult), immediately after the response status and header assertions, as the following example shows:

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 can consume the Flux<T>, assert decoded objects as they come, and then cancel at some point when test objectives are met. We recommend using the StepVerifier from the reactor-test module to do that, as the following example shows:

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()

Request Body

When it comes to building requests, the WebTestClient offers an API identical to the WebClient, and the implementation is mostly a simple pass-through. See the WebClient documentation for examples on how to prepare a request with a body, including submitting form data, multipart requests, and more.