Add JUnit 5 checkstyle rules

Add a rule to enforce JUnit 5 usage and conventions.

Closes gh-17093

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/test/autoconfigure/restdocs/restassured/UserDocumentationTests.java

@@ -19,33 +19,24 @@ package org.springframework.boot.docs.test.autoconfigure.restdocs.restassured;
 // tag::source[]
 import io.restassured.specification.RequestSpecification;
 import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.extension.ExtendWith;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
 import org.springframework.boot.web.server.LocalServerPort;
-import org.springframework.test.context.junit.jupiter.SpringExtension;
 
 import static io.restassured.RestAssured.given;
 import static org.hamcrest.Matchers.is;
 import static org.springframework.restdocs.restassured3.RestAssuredRestDocumentation.document;
 
-@ExtendWith(SpringExtension.class)
 @SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
 @AutoConfigureRestDocs
-public class UserDocumentationTests {
-
-	@LocalServerPort
-	private int port;
-
-	@Autowired
-	private RequestSpecification documentationSpec;
+class UserDocumentationTests {
 
 	@Test
-	public void listUsers() {
-		given(this.documentationSpec).filter(document("list-users")).when().port(this.port).get("/").then().assertThat()
+	void listUsers(@Autowired RequestSpecification documentationSpec, @LocalServerPort int port) {
+		given(documentationSpec).filter(document("list-users")).when().port(port).get("/").then().assertThat()
 				.statusCode(is(200));
 	}
 

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/test/context/ApplicationArgumentsExampleTests.java

@@ -17,27 +17,21 @@
 package org.springframework.boot.docs.test.context;
 
 import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.extension.ExtendWith;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.ApplicationArguments;
 import org.springframework.boot.test.context.SpringBootTest;
-import org.springframework.test.context.junit.jupiter.SpringExtension;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 // tag::example[]
-@ExtendWith(SpringExtension.class)
 @SpringBootTest(args = "--app.test=one")
-public class ApplicationArgumentsExampleTests {
-
-	@Autowired
-	private ApplicationArguments args;
+class ApplicationArgumentsExampleTests {
 
 	@Test
-	public void applicationArgumentsPopulated() {
-		assertThat(this.args.getOptionNames()).containsOnly("app.test");
-		assertThat(this.args.getOptionValues("app.test")).containsOnly("one");
+	void applicationArgumentsPopulated(@Autowired ApplicationArguments args) {
+		assertThat(args.getOptionNames()).containsOnly("app.test");
+		assertThat(args.getOptionValues("app.test")).containsOnly("one");
 	}
 
 }

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/test/web/MockMvcExampleTests.java

@@ -19,29 +19,22 @@ package org.springframework.boot.docs.test.web;
 // tag::test-mock-mvc[]
 
 import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.extension.ExtendWith;
 
-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.context.junit.jupiter.SpringExtension;
 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;
 
-@ExtendWith(SpringExtension.class)
 @SpringBootTest
 @AutoConfigureMockMvc
-public class MockMvcExampleTests {
-
-	@Autowired
-	private MockMvc mvc;
+class MockMvcExampleTests {
 
 	@Test
-	public void exampleTest() throws Exception {
-		this.mvc.perform(get("/")).andExpect(status().isOk()).andExpect(content().string("Hello World"));
+	void exampleTest(MockMvc mvc) throws Exception {
+		mvc.perform(get("/")).andExpect(status().isOk()).andExpect(content().string("Hello World"));
 	}
 
 }

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/test/web/MockWebTestClientExampleTests.java

@@ -19,26 +19,19 @@ package org.springframework.boot.docs.test.web;
 // tag::test-mock-web-test-client[]
 
 import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.extension.ExtendWith;
 
 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.context.junit.jupiter.SpringExtension;
 import org.springframework.test.web.reactive.server.WebTestClient;
 
-@ExtendWith(SpringExtension.class)
 @SpringBootTest
 @AutoConfigureWebTestClient
-public class MockWebTestClientExampleTests {
-
-	@Autowired
-	private WebTestClient webClient;
+class MockWebTestClientExampleTests {
 
 	@Test
-	public void exampleTest() {
-		this.webClient.get().uri("/").exchange().expectStatus().isOk().expectBody(String.class)
-				.isEqualTo("Hello World");
+	void exampleTest(@Autowired WebTestClient webClient) {
+		webClient.get().uri("/").exchange().expectStatus().isOk().expectBody(String.class).isEqualTo("Hello World");
 	}
 
 }

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/test/web/RandomPortTestRestTemplateExampleTests.java

@@ -19,26 +19,20 @@ package org.springframework.boot.docs.test.web;
 // tag::test-random-port[]
 
 import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.extension.ExtendWith;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
 import org.springframework.boot.test.web.client.TestRestTemplate;
-import org.springframework.test.context.junit.jupiter.SpringExtension;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
-@ExtendWith(SpringExtension.class)
 @SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
-public class RandomPortTestRestTemplateExampleTests {
-
-	@Autowired
-	private TestRestTemplate restTemplate;
+class RandomPortTestRestTemplateExampleTests {
 
 	@Test
-	public void exampleTest() {
-		String body = this.restTemplate.getForObject("/", String.class);
+	void exampleTest(@Autowired TestRestTemplate restTemplate) {
+		String body = restTemplate.getForObject("/", String.class);
 		assertThat(body).isEqualTo("Hello World");
 	}
 

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/test/web/RandomPortWebTestClientExampleTests.java

@@ -19,25 +19,18 @@ package org.springframework.boot.docs.test.web;
 // tag::test-random-port[]
 
 import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.extension.ExtendWith;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
-import org.springframework.test.context.junit.jupiter.SpringExtension;
 import org.springframework.test.web.reactive.server.WebTestClient;
 
-@ExtendWith(SpringExtension.class)
 @SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
 public class RandomPortWebTestClientExampleTests {
 
-	@Autowired
-	private WebTestClient webClient;
-
 	@Test
-	public void exampleTest() {
-		this.webClient.get().uri("/").exchange().expectStatus().isOk().expectBody(String.class)
-				.isEqualTo("Hello World");
+	void exampleTest(@Autowired WebTestClient webClient) {
+		webClient.get().uri("/").exchange().expectStatus().isOk().expectBody(String.class).isEqualTo("Hello World");
 	}
 
 }