Testing With a Mock Environment

By default, @SpringBootTest does not start the server but instead sets up a mock environment for testing web endpoints.

With Spring MVC, we can query our web endpoints using MockMvc or WebTestClient, as shown in the following example:

Java
Kotlin

import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.web.reactive.server.WebTestClient;
import org.springframework.test.web.servlet.MockMvc;

import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@SpringBootTest
@AutoConfigureMockMvc
class MyMockMvcTests {

	@Test
	void testWithMockMvc(@Autowired MockMvc mvc) throws Exception {
		mvc.perform(get("/")).andExpect(status().isOk()).andExpect(content().string("Hello World"));
	}

	// If Spring WebFlux is on the classpath, you can drive MVC tests with a WebTestClient
	@Test
	void testWithWebTestClient(@Autowired WebTestClient webClient) {
		webClient
				.get().uri("/")
				.exchange()
				.expectStatus().isOk()
				.expectBody(String.class).isEqualTo("Hello World");
	}

}

import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.test.web.reactive.server.WebTestClient
import org.springframework.test.web.reactive.server.expectBody
import org.springframework.test.web.servlet.MockMvc
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders
import org.springframework.test.web.servlet.result.MockMvcResultMatchers

@SpringBootTest
@AutoConfigureMockMvc
class MyMockMvcTests {

	@Test
	fun testWithMockMvc(@Autowired mvc: MockMvc) {
		mvc.perform(MockMvcRequestBuilders.get("/")).andExpect(MockMvcResultMatchers.status().isOk)
			.andExpect(MockMvcResultMatchers.content().string("Hello World"))
	}

	// If Spring WebFlux is on the classpath, you can drive MVC tests with a WebTestClient

	@Test
	fun testWithWebTestClient(@Autowired webClient: WebTestClient) {
		webClient
			.get().uri("/")
			.exchange()
			.expectStatus().isOk
			.expectBody<String>().isEqualTo("Hello World")
	}

}

If you want to focus only on the web layer and not start a complete ApplicationContext, consider using @WebMvcTest instead.

With Spring WebFlux endpoints, you can use WebTestClient as shown in the following example:

Java
Kotlin

import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebTestClient;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.web.reactive.server.WebTestClient;

@SpringBootTest
@AutoConfigureWebTestClient
class MyMockWebTestClientTests {

	@Test
	void exampleTest(@Autowired WebTestClient webClient) {
		webClient
			.get().uri("/")
			.exchange()
			.expectStatus().isOk()
			.expectBody(String.class).isEqualTo("Hello World");
	}

}

import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebTestClient
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.test.web.reactive.server.WebTestClient
import org.springframework.test.web.reactive.server.expectBody

@SpringBootTest
@AutoConfigureWebTestClient
class MyMockWebTestClientTests {

	@Test
	fun exampleTest(@Autowired webClient: WebTestClient) {
		webClient
			.get().uri("/")
			.exchange()
			.expectStatus().isOk
			.expectBody<String>().isEqualTo("Hello World")
	}

}

Testing within a mocked environment is usually faster than running with a full servlet container. However, since mocking occurs at the Spring MVC layer, code that relies on lower-level servlet container behavior cannot be directly tested with MockMvc.

For example, Spring Boot’s error handling is based on the “error page” support provided by the servlet container. This means that, whilst you can test your MVC layer throws and handles exceptions as expected, you cannot directly test that a specific custom error page is rendered. If you need to test these lower-level concerns, you can start a fully running server as described in the next section.