Remove mentions of JUnit 4

This commit removes all mentions of JUnit 4 from the Javadoc and
reference documentation. It also harmonizes to simply refers to JUnit.

Closes gh-47228

Author: snicoll

build-plugin/spring-boot-gradle-plugin/src/docs/antora/modules/gradle-plugin/pages/aot.adoc

@@ -44,7 +44,7 @@ The `nativeCompile` task of the GraalVM Native Image plugin is automatically con
 [[aot.processing-tests]]
 == Processing Tests
 
-The AOT engine can be applied to JUnit 5 tests that use Spring's Test Context Framework.
+The AOT engine can be applied to JUnit tests that use Spring's Test Context Framework.
 Suitable tests are processed by the `processTestAot` task to generate `ApplicationContextInitializer` code.
 As with application AOT processing, the `BeanFactory` is fully prepared at build-time.
 As with `processAot`, the `processTestAot` task is `JavaExec` subclass and can be configured as needed to influence this processing.

build-plugin/spring-boot-maven-plugin/src/docs/antora/modules/maven-plugin/pages/aot.adoc

@@ -89,7 +89,7 @@ include::partial$goals/process-aot.adoc[leveloffset=+1]
 [[aot.processing-tests]]
 == Processing Tests
 
-The AOT engine can be applied to JUnit 5 tests that use Spring's Test Context Framework.
+The AOT engine can be applied to JUnit tests that use Spring's Test Context Framework.
 Those tests are processed by the AOT engine and are then executed in a native image.
 
 Just like <<aot.processing-applications.using-the-native-profile,for production code>>, the `spring-boot-starter-parent` defines a `nativeTest` profile that can be used to streamline the steps required to execute your tests in a native image.

core/spring-boot-test/src/test/java/org/springframework/boot/test/context/filter/TestTypeExcludeFilterTests.java

@@ -40,6 +40,7 @@ class TestTypeExcludeFilterTests {
 	private final MetadataReaderFactory metadataReaderFactory = new SimpleMetadataReaderFactory();
 
 	@Test
+	@Deprecated(since = "4.0.0")
 	void matchesJUnit4TestClass() throws Exception {
 		assertThat(this.filter.match(getMetadataReader(TestTypeExcludeFilterTests.class), this.metadataReaderFactory))
 			.isTrue();

core/spring-boot/src/main/java/org/springframework/boot/context/annotation/Configurations.java

@@ -49,7 +49,7 @@
  * {@link ApplicationContext} and/or custom {@link ImportSelector} implementations.
  * <p>
  * This class is primarily intended for use with tests that need to specify configuration
- * classes but can't use {@link org.springframework.test.context.junit4.SpringRunner}.
+ * classes.
  * <p>
  * Implementations of this class should be annotated with {@link Order @Order} or
  * implement {@link Ordered}.

documentation/spring-boot-docs/src/docs/antora/modules/reference/pages/features/kotlin.adoc

@@ -142,8 +142,7 @@ Note that some features (such as detecting the default value or deprecated items
 [[features.kotlin.testing]]
 == Testing
 
-While it is possible to use JUnit 4 to test Kotlin code, JUnit 5 is provided by default and is recommended.
-JUnit 5 enables a test class to be instantiated once and reused for all of the class's tests.
+JUnit enables a test class to be instantiated once and reused for all of the class's tests.
 This makes it possible to use javadoc:org.junit.jupiter.api.BeforeAll[format=annotation] and javadoc:org.junit.jupiter.api.AfterAll[format=annotation] annotations on non-static methods, which is a good fit for Kotlin.
 
 To mock Kotlin classes, https://mockk.io/[MockK] is recommended.

documentation/spring-boot-docs/src/docs/antora/modules/reference/pages/testing/index.adoc

@@ -8,7 +8,7 @@ Most developers use the `spring-boot-starter-test` starter, which imports both S
 
 [TIP]
 ====
-If you have tests that use JUnit 4, JUnit 5's vintage engine can be used to run them.
+If you have tests that still use JUnit 4, JUnit's vintage engine can be used to run them.
 To use the vintage engine, add a dependency on `junit-vintage-engine`, as shown in the following example:
 
 [source,xml]

documentation/spring-boot-docs/src/docs/antora/modules/reference/pages/testing/spring-boot-applications.adoc

@@ -9,8 +9,7 @@ Spring Boot provides a javadoc:org.springframework.boot.test.context.SpringBootT
 The annotation works by xref:testing/spring-boot-applications.adoc#testing.spring-boot-applications.detecting-configuration[creating the javadoc:org.springframework.context.ApplicationContext[] used in your tests through javadoc:org.springframework.boot.SpringApplication[]].
 In addition to javadoc:org.springframework.boot.test.context.SpringBootTest[format=annotation] a number of other annotations are also provided for xref:testing/spring-boot-applications.adoc#testing.spring-boot-applications.autoconfigured-tests[testing more specific slices] of an application.
 
-TIP: If you are using JUnit 4, do not forget to also add `@RunWith(SpringRunner.class)` to your test, otherwise the annotations will be ignored.
-If you are using JUnit 5, there is no need to add the equivalent `@ExtendWith(SpringExtension.class)` as javadoc:org.springframework.boot.test.context.SpringBootTest[format=annotation] and the other `@...Test` annotations are already annotated with it.
+If you are using JUnit, there is no need to add the equivalent `@ExtendWith(SpringExtension.class)` as javadoc:org.springframework.boot.test.context.SpringBootTest[format=annotation] and the other `@...Test` annotations are already annotated with it.
 
 By default, javadoc:org.springframework.boot.test.context.SpringBootTest[format=annotation] will not start a server.
 You can use the `webEnvironment` attribute of javadoc:org.springframework.boot.test.context.SpringBootTest[format=annotation] to further refine how your tests run:

documentation/spring-boot-docs/src/docs/antora/modules/reference/pages/testing/test-scope-dependencies.adoc

@@ -3,7 +3,7 @@
 
 The `spring-boot-starter-test` starter (in the `test` `scope`) contains the following provided libraries:
 
-* https://junit.org/junit5/[JUnit 5]: The de-facto standard for unit testing Java applications.
+* https://junit.org/junit5/[JUnit]: The de-facto standard for unit testing Java applications.
 * {url-spring-framework-docs}/testing/integration.html[Spring Test] & Spring Boot Test: Utilities and integration test support for Spring Boot applications.
 * https://assertj.github.io/doc/[AssertJ]: A fluent assertion library.
 * https://github.com/hamcrest/JavaHamcrest[Hamcrest]: A library of matcher objects (also known as constraints or predicates).

loader/spring-boot-loader-classic/src/test/java/org/springframework/boot/loader/jar/JarUrlProtocolHandler.java

@@ -28,9 +28,9 @@
 import org.springframework.test.util.ReflectionTestUtils;
 
 /**
- * JUnit 5 {@link Extension} for tests that interact with Spring Boot's {@link Handler}
- * for {@code jar:} URLs. Ensures that the handler is registered prior to test execution
- * and cleans up the handler's root file cache afterwards.
+ * JUnit {@link Extension} for tests that interact with Spring Boot's {@link Handler} for
+ * {@code jar:} URLs. Ensures that the handler is registered prior to test execution and
+ * cleans up the handler's root file cache afterwards.
  *
  * @author Andy Wilkinson
  */

module/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/data/cassandra/DataCassandraTest.java

@@ -43,9 +43,6 @@
  * Using this annotation only enables auto-configuration that is relevant to Data Casandra
  * tests. Similarly, component scanning is limited to Cassandra repositories and entities
  * ({@code @Table}).
- * <p>
- * When using JUnit 4, this annotation should be used in combination with
- * {@code @RunWith(SpringRunner.class)}.
  *
  * @author Artsiom Yudovin
  * @author Stephane Nicoll