Ensure that a test engine is available to AOT test processing

See gh-32192

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/SpringBootAotPlugin.java

@@ -86,7 +86,8 @@ public class SpringBootAotPlugin implements Plugin<Project> {
 		return sourceSets.create(newSourceSetName, (sourceSet) -> {
 			sourceSet.getJava().setSrcDirs(List.of("build/generated/" + newSourceSetName + "Sources"));
 			sourceSet.getResources().setSrcDirs(List.of("build/generated/" + newSourceSetName + "Resources"));
-			sourceSet.setCompileClasspath(sourceSet.getCompileClasspath().plus(existingSourceSet.getOutput()));
+			sourceSet.setCompileClasspath(sourceSet.getCompileClasspath().plus(existingSourceSet.getCompileClasspath())
+					.plus(existingSourceSet.getOutput()));
 			existingSourceSet.setRuntimeClasspath(existingSourceSet.getRuntimeClasspath().plus(sourceSet.getOutput()));
 			ConfigurationContainer configurations = project.getConfigurations();
 			Configuration implementation = configurations.getByName(sourceSet.getImplementationConfigurationName());
@@ -151,7 +152,7 @@ public class SpringBootAotPlugin implements Plugin<Project> {
 				ProcessTestAot.class, (task) -> {
 					configureAotTask(project, aotTestSourceSet, task,
 							project.getLayout().getBuildDirectory().dir("generated/aotTestClasses"));
-					task.setTestClassesDirs(testSourceSet.getOutput().getClassesDirs());
+					task.setTestSourceSet(testSourceSet);
 				});
 		configureDependsOn(project, aotTestSourceSet, processTestAot);
 	}

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/tasks/aot/ProcessTestAot.java

@@ -29,6 +29,7 @@ import org.gradle.api.file.FileCollection;
 import org.gradle.api.tasks.CacheableTask;
 import org.gradle.api.tasks.Classpath;
 import org.gradle.api.tasks.JavaExec;
+import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.TaskAction;
 
 import org.springframework.boot.gradle.plugin.SpringBootPlugin;
@@ -42,7 +43,7 @@ import org.springframework.boot.gradle.plugin.SpringBootPlugin;
 @CacheableTask
 public class ProcessTestAot extends AbstractAot {
 
-	private final FileCollection junitPlatformLauncher;
+	private final Configuration junitPlatformLauncher;
 
 	private FileCollection testClassesDirs;
 
@@ -84,7 +85,14 @@ public class ProcessTestAot extends AbstractAot {
 				.collect(Collectors.joining(File.pathSeparator)));
 		args.addAll(processorArgs());
 		this.setArgs(args);
+		this.classpath(this.junitPlatformLauncher);
 		super.exec();
 	}
 
+	public void setTestSourceSet(SourceSet testSourceSet) {
+		setTestClassesDirs(testSourceSet.getOutput().getClassesDirs());
+		this.junitPlatformLauncher.extendsFrom(
+				getProject().getConfigurations().getByName(testSourceSet.getImplementationConfigurationName()));
+	}
+
 }