Split up JUnit 5 OutputCapture class

Split the JUnit 5 `OutputCapture` class into separate `OutputExtension`
and `CapturedOutput` classes. The JUnit 5 callback methods are now
contained only in the `OutputExtension` class so no longer pollute the
public API that users will interact with.

The `CapturedOutput` class has also been updated to capture System.err
and System.out separately to allow distinct assertions if required.

Closes gh-17029

Author: philwebb

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/export/prometheus/PrometheusMetricsExportAutoConfigurationTests.java

@@ -29,7 +29,8 @@
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.test.context.assertj.AssertableApplicationContext;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
-import org.springframework.boot.test.extension.OutputCapture;
+import org.springframework.boot.test.extension.CapturedOutput;
+import org.springframework.boot.test.extension.OutputExtension;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
@@ -45,7 +46,7 @@
 public class PrometheusMetricsExportAutoConfigurationTests {
 
 	@RegisterExtension
-	public OutputCapture output = new OutputCapture();
+	CapturedOutput output = OutputExtension.capture();
 
 	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
 			.withConfiguration(AutoConfigurations

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/web/client/RestTemplateMetricsConfigurationTests.java

@@ -29,7 +29,8 @@
 import org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration;
 import org.springframework.boot.test.context.assertj.AssertableApplicationContext;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
-import org.springframework.boot.test.extension.OutputCapture;
+import org.springframework.boot.test.extension.CapturedOutput;
+import org.springframework.boot.test.extension.OutputExtension;
 import org.springframework.boot.web.client.RestTemplateBuilder;
 import org.springframework.http.HttpStatus;
 import org.springframework.test.web.client.MockRestServiceServer;
@@ -54,7 +55,7 @@ public class RestTemplateMetricsConfigurationTests {
 					HttpClientMetricsAutoConfiguration.class));
 
 	@RegisterExtension
-	public OutputCapture output = new OutputCapture();
+	CapturedOutput output = OutputExtension.capture();
 
 	@Test
 	public void restTemplateCreatedWithBuilderIsInstrumented() {

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/web/client/WebClientMetricsConfigurationTests.java

@@ -31,7 +31,8 @@
 import org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration;
 import org.springframework.boot.test.context.assertj.AssertableApplicationContext;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
-import org.springframework.boot.test.extension.OutputCapture;
+import org.springframework.boot.test.extension.CapturedOutput;
+import org.springframework.boot.test.extension.OutputExtension;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.http.HttpStatus;
@@ -58,7 +59,7 @@ public class WebClientMetricsConfigurationTests {
 					HttpClientMetricsAutoConfiguration.class));
 
 	@RegisterExtension
-	public OutputCapture output = new OutputCapture();
+	CapturedOutput output = OutputExtension.capture();
 
 	@Test
 	public void webClientCreatedWithBuilderIsInstrumented() {

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/web/reactive/WebFluxMetricsAutoConfigurationTests.java

@@ -29,7 +29,8 @@
 import org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration;
 import org.springframework.boot.test.context.assertj.AssertableReactiveWebApplicationContext;
 import org.springframework.boot.test.context.runner.ReactiveWebApplicationContextRunner;
-import org.springframework.boot.test.extension.OutputCapture;
+import org.springframework.boot.test.extension.CapturedOutput;
+import org.springframework.boot.test.extension.OutputExtension;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.test.web.reactive.server.WebTestClient;
@@ -50,7 +51,7 @@ public class WebFluxMetricsAutoConfigurationTests {
 					AutoConfigurations.of(WebFluxMetricsAutoConfiguration.class));
 
 	@RegisterExtension
-	public OutputCapture output = new OutputCapture();
+	CapturedOutput output = OutputExtension.capture();
 
 	@Test
 	public void shouldProvideWebFluxMetricsBeans() {

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/web/servlet/WebMvcMetricsAutoConfigurationTests.java

@@ -42,7 +42,8 @@
 import org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration;
 import org.springframework.boot.test.context.assertj.AssertableWebApplicationContext;
 import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
-import org.springframework.boot.test.extension.OutputCapture;
+import org.springframework.boot.test.extension.CapturedOutput;
+import org.springframework.boot.test.extension.OutputExtension;
 import org.springframework.boot.web.servlet.FilterRegistrationBean;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -69,7 +70,7 @@ public class WebMvcMetricsAutoConfigurationTests {
 					AutoConfigurations.of(WebMvcMetricsAutoConfiguration.class));
 
 	@RegisterExtension
-	public OutputCapture output = new OutputCapture();
+	CapturedOutput output = OutputExtension.capture();
 
 	@Test
 	public void backsOffWhenMeterRegistryIsMissing() {

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/web/server/ManagementContextAutoConfigurationTests.java

@@ -27,7 +27,8 @@
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration;
 import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
-import org.springframework.boot.test.extension.OutputCapture;
+import org.springframework.boot.test.extension.CapturedOutput;
+import org.springframework.boot.test.extension.OutputExtension;
 import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -41,7 +42,7 @@
 public class ManagementContextAutoConfigurationTests {
 
 	@RegisterExtension
-	public OutputCapture output = new OutputCapture();
+	CapturedOutput output = OutputExtension.capture();
 
 	@Test
 	public void childManagementContextShouldStartForEmbeddedServer() {

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/EndpointIdTests.java

@@ -19,7 +19,8 @@
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.RegisterExtension;
 
-import org.springframework.boot.test.extension.OutputCapture;
+import org.springframework.boot.test.extension.CapturedOutput;
+import org.springframework.boot.test.extension.OutputExtension;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
@@ -32,7 +33,7 @@
 public class EndpointIdTests {
 
 	@RegisterExtension
-	public OutputCapture output = new OutputCapture();
+	CapturedOutput output = OutputExtension.capture();
 
 	@Test
 	public void ofWhenNullThrowsException() {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/freemarker/FreeMarkerAutoConfigurationTests.java

@@ -24,7 +24,8 @@
 
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
-import org.springframework.boot.test.extension.OutputCapture;
+import org.springframework.boot.test.extension.CapturedOutput;
+import org.springframework.boot.test.extension.OutputExtension;
 import org.springframework.boot.testsupport.BuildOutput;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -38,7 +39,7 @@
 public class FreeMarkerAutoConfigurationTests {
 
 	@RegisterExtension
-	public OutputCapture output = new OutputCapture();
+	CapturedOutput output = OutputExtension.capture();
 
 	private final BuildOutput buildOutput = new BuildOutput(getClass());
 

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/influx/InfluxDbAutoConfigurationTests.java

@@ -27,7 +27,8 @@
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.test.context.assertj.AssertableApplicationContext;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
-import org.springframework.boot.test.extension.OutputCapture;
+import org.springframework.boot.test.extension.CapturedOutput;
+import org.springframework.boot.test.extension.OutputExtension;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.test.util.ReflectionTestUtils;
@@ -44,7 +45,7 @@
 public class InfluxDbAutoConfigurationTests {
 
 	@RegisterExtension
-	public OutputCapture output = new OutputCapture();
+	CapturedOutput output = OutputExtension.capture();
 
 	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
 			.withConfiguration(AutoConfigurations.of(InfluxDbAutoConfiguration.class));

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jersey/JerseyAutoConfigurationServletContainerTests.java

@@ -36,7 +36,8 @@
 import org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
-import org.springframework.boot.test.extension.OutputCapture;
+import org.springframework.boot.test.extension.CapturedOutput;
+import org.springframework.boot.test.extension.OutputExtension;
 import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -53,11 +54,11 @@
  */
 @SpringBootTest(classes = Application.class, webEnvironment = WebEnvironment.RANDOM_PORT)
 @DirtiesContext
-@ExtendWith(OutputCapture.class)
+@ExtendWith(OutputExtension.class)
 public class JerseyAutoConfigurationServletContainerTests {
 
 	@Test
-	public void existingJerseyServletIsAmended(OutputCapture output) {
+	public void existingJerseyServletIsAmended(CapturedOutput output) {
 		assertThat(output)
 				.contains("Configuring existing registration for Jersey servlet");
 		assertThat(output).contains(