Allow tests to be run in parallel across multiple workers

Closes gh-19876

buildSrc/src/main/java/org/springframework/boot/build/JavaConventions.java

@@ -156,6 +156,7 @@ class JavaConventions {
 		project.getTasks().withType(Test.class, (test) -> {
 			test.useJUnitPlatform();
 			test.setMaxHeapSize("1024M");
+			test.setMaxParallelForks(project.getGradle().getStartParameter().getMaxWorkerCount());
 			project.getTasks().withType(Checkstyle.class, (checkstyle) -> test.mustRunAfter(checkstyle));
 			project.getTasks().withType(CheckFormat.class, (checkFormat) -> test.mustRunAfter(checkFormat));
 		});

spring-boot-tests/spring-boot-integration-tests/spring-boot-server-tests/src/intTest/java/org/springframework/boot/context/embedded/AbstractApplicationLauncher.java

@@ -29,8 +29,8 @@ import org.awaitility.Awaitility;
 import org.junit.jupiter.api.extension.BeforeEachCallback;
 import org.junit.jupiter.api.extension.ExtensionContext;
 
-import org.springframework.boot.testsupport.BuildOutput;
 import org.springframework.util.FileCopyUtils;
+import org.springframework.util.FileSystemUtils;
 import org.springframework.util.StreamUtils;
 import org.springframework.util.StringUtils;
 
@@ -43,15 +43,15 @@ abstract class AbstractApplicationLauncher implements BeforeEachCallback {
 
 	private final Application application;
 
-	private final BuildOutput buildOutput;
+	private final File outputLocation;
 
 	private Process process;
 
 	private int httpPort;
 
-	protected AbstractApplicationLauncher(Application application, BuildOutput buildOutput) {
+	protected AbstractApplicationLauncher(Application application, File outputLocation) {
 		this.application = application;
-		this.buildOutput = buildOutput;
+		this.outputLocation = outputLocation;
 	}
 
 	@Override
@@ -71,6 +71,7 @@ abstract class AbstractApplicationLauncher implements BeforeEachCallback {
 				Thread.currentThread().interrupt();
 			}
 		}
+		FileSystemUtils.deleteRecursively(this.outputLocation);
 	}
 
 	final int getHttpPort() {
@@ -85,7 +86,7 @@ abstract class AbstractApplicationLauncher implements BeforeEachCallback {
 
 	private Process startApplication() throws Exception {
 		File workingDirectory = getWorkingDirectory();
-		File serverPortFile = new File(this.buildOutput.getRootLocation(), "server.port");
+		File serverPortFile = new File(this.outputLocation, "server.port");
 		serverPortFile.delete();
 		File archive = new File("build/spring-boot-server-tests-app/build/libs/spring-boot-server-tests-app-"
 				+ this.application.getContainer() + "." + this.application.getPackaging());

spring-boot-tests/spring-boot-integration-tests/spring-boot-server-tests/src/intTest/java/org/springframework/boot/context/embedded/BootRunApplicationLauncher.java

@@ -27,7 +27,6 @@ import java.util.List;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 
-import org.springframework.boot.testsupport.BuildOutput;
 import org.springframework.util.FileCopyUtils;
 import org.springframework.util.FileSystemUtils;
 import org.springframework.util.StreamUtils;
@@ -43,9 +42,9 @@ class BootRunApplicationLauncher extends AbstractApplicationLauncher {
 
 	private final File exploded;
 
-	BootRunApplicationLauncher(Application application, BuildOutput buildOutput) {
-		super(application, buildOutput);
-		this.exploded = new File(buildOutput.getRootLocation(), "run");
+	BootRunApplicationLauncher(Application application, File outputLocation) {
+		super(application, outputLocation);
+		this.exploded = new File(outputLocation, "run");
 	}
 
 	@Override

spring-boot-tests/spring-boot-integration-tests/spring-boot-server-tests/src/intTest/java/org/springframework/boot/context/embedded/EmbeddedServerContainerInvocationContextProvider.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.context.embedded;
 
+import java.io.File;
 import java.io.IOException;
 import java.net.URI;
 import java.nio.file.Files;
@@ -26,6 +27,7 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.UUID;
 import java.util.stream.Stream;
 
 import org.apache.http.impl.client.HttpClients;
@@ -110,7 +112,8 @@ class EmbeddedServerContainerInvocationContextProvider
 		if (this.launcherCache.containsKey(cacheKey)) {
 			return this.launcherCache.get(cacheKey);
 		}
-		AbstractApplicationLauncher launcher = ReflectionUtils.newInstance(launcherClass, application, buildOutput);
+		AbstractApplicationLauncher launcher = ReflectionUtils.newInstance(launcherClass, application,
+				new File(buildOutput.getRootLocation(), "app-launcher-" + UUID.randomUUID()));
 		this.launcherCache.put(cacheKey, launcher);
 		return launcher;
 	}

spring-boot-tests/spring-boot-integration-tests/spring-boot-server-tests/src/intTest/java/org/springframework/boot/context/embedded/ExplodedApplicationLauncher.java

@@ -22,11 +22,9 @@ import java.io.IOException;
 import java.util.Arrays;
 import java.util.Enumeration;
 import java.util.List;
-import java.util.function.Supplier;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 
-import org.springframework.boot.testsupport.BuildOutput;
 import org.springframework.util.FileSystemUtils;
 import org.springframework.util.StreamUtils;
 
@@ -38,16 +36,16 @@ import org.springframework.util.StreamUtils;
  */
 class ExplodedApplicationLauncher extends AbstractApplicationLauncher {
 
-	private final Supplier<File> exploded;
+	private final File exploded;
 
-	ExplodedApplicationLauncher(Application application, BuildOutput buildOutput) {
-		super(application, buildOutput);
-		this.exploded = () -> new File(buildOutput.getRootLocation(), "exploded");
+	ExplodedApplicationLauncher(Application application, File outputLocation) {
+		super(application, outputLocation);
+		this.exploded = new File(outputLocation, "exploded");
 	}
 
 	@Override
 	protected File getWorkingDirectory() {
-		return this.exploded.get();
+		return this.exploded;
 	}
 
 	@Override
@@ -61,8 +59,7 @@ class ExplodedApplicationLauncher extends AbstractApplicationLauncher {
 				: "org.springframework.boot.loader.JarLauncher");
 		try {
 			explodeArchive(archive);
-			return Arrays.asList("-cp", this.exploded.get().getAbsolutePath(), mainClass,
-					serverPortFile.getAbsolutePath());
+			return Arrays.asList("-cp", this.exploded.getAbsolutePath(), mainClass, serverPortFile.getAbsolutePath());
 		}
 		catch (IOException ex) {
 			throw new RuntimeException(ex);
@@ -70,12 +67,12 @@ class ExplodedApplicationLauncher extends AbstractApplicationLauncher {
 	}
 
 	private void explodeArchive(File archive) throws IOException {
-		FileSystemUtils.deleteRecursively(this.exploded.get());
+		FileSystemUtils.deleteRecursively(this.exploded);
 		JarFile jarFile = new JarFile(archive);
 		Enumeration<JarEntry> entries = jarFile.entries();
 		while (entries.hasMoreElements()) {
 			JarEntry jarEntry = entries.nextElement();
-			File extracted = new File(this.exploded.get(), jarEntry.getName());
+			File extracted = new File(this.exploded, jarEntry.getName());
 			if (jarEntry.isDirectory()) {
 				extracted.mkdirs();
 			}

spring-boot-tests/spring-boot-integration-tests/spring-boot-server-tests/src/intTest/java/org/springframework/boot/context/embedded/IdeApplicationLauncher.java

@@ -27,7 +27,6 @@ import java.util.List;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 
-import org.springframework.boot.testsupport.BuildOutput;
 import org.springframework.util.FileCopyUtils;
 import org.springframework.util.FileSystemUtils;
 import org.springframework.util.StreamUtils;
@@ -43,9 +42,9 @@ class IdeApplicationLauncher extends AbstractApplicationLauncher {
 
 	private final File exploded;
 
-	IdeApplicationLauncher(Application application, BuildOutput buildOutput) {
-		super(application, buildOutput);
-		this.exploded = new File(buildOutput.getRootLocation(), "the+ide application");
+	IdeApplicationLauncher(Application application, File outputLocation) {
+		super(application, outputLocation);
+		this.exploded = new File(outputLocation, "the+ide application");
 	}
 
 	@Override

spring-boot-tests/spring-boot-integration-tests/spring-boot-server-tests/src/intTest/java/org/springframework/boot/context/embedded/PackagedApplicationLauncher.java

@@ -20,8 +20,6 @@ import java.io.File;
 import java.util.Arrays;
 import java.util.List;
 
-import org.springframework.boot.testsupport.BuildOutput;
-
 /**
  * {@link AbstractApplicationLauncher} that launches a packaged Spring Boot application
  * using {@code java -jar}.
@@ -30,8 +28,8 @@ import org.springframework.boot.testsupport.BuildOutput;
  */
 class PackagedApplicationLauncher extends AbstractApplicationLauncher {
 
-	PackagedApplicationLauncher(Application application, BuildOutput buildOutput) {
-		super(application, buildOutput);
+	PackagedApplicationLauncher(Application application, File outputLocation) {
+		super(application, outputLocation);
 	}
 
 	@Override