Introduce CLI for triggering AOT test context processing

This commit introduces ProcessTestsAheadOfTimeCommand, a command-line
application (CLI) that scans the provided classpath roots for Spring
integration test classes and then generates AOT artifacts for those
test classes in the provided output directories.

This CLI is only intended to be used by build tools.

Closes gh-28825

spring-test/src/test/java/org/springframework/test/context/aot/AbstractAotTests.java

@@ -72,7 +72,16 @@ abstract class AbstractAotTests {
 
 	Set<Path> classpathRoots() {
 		try {
-			return Set.of(Paths.get(getClass().getProtectionDomain().getCodeSource().getLocation().toURI()));
+			return Set.of(classpathRoot());
+		}
+		catch (Exception ex) {
+			throw new RuntimeException(ex);
+		}
+	}
+
+	Path classpathRoot() {
+		try {
+			return Paths.get(getClass().getProtectionDomain().getCodeSource().getLocation().toURI());
 		}
 		catch (Exception ex) {
 			throw new RuntimeException(ex);

spring-test/src/test/java/org/springframework/test/context/aot/ProcessTestsAheadOfTimeCommandTests.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2002-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.test.context.aot;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.CleanupMode;
+import org.junit.jupiter.api.io.TempDir;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link ProcessTestsAheadOfTimeCommand}.
+ *
+ * @author Sam Brannen
+ * @since 6.0
+ */
+class ProcessTestsAheadOfTimeCommandTests extends AbstractAotTests {
+
+	@Test
+	void execute(@TempDir(cleanup = CleanupMode.ON_SUCCESS) Path tempDir) throws Exception {
+		Path sourcesOutputPath = tempDir.resolve("src/test/java").toAbsolutePath();
+		Path resourcesOutputPath = tempDir.resolve("src/test/resources").toAbsolutePath();
+		String testPackage = "org.springframework.test.context.aot.samples.basic";
+		String[] args = {
+				"--sources-out=" + sourcesOutputPath,
+				"--resources-out=" + resourcesOutputPath,
+				"--packages=" + testPackage,
+				classpathRoot().toString()
+			};
+		int exitCode = ProcessTestsAheadOfTimeCommand.execute(args);
+		assertThat(exitCode).as("exit code").isZero();
+
+		assertThat(findFiles(sourcesOutputPath)).containsExactlyInAnyOrder(
+				expectedSourceFilesForBasicSpringTests);
+
+		assertThat(findFiles(resourcesOutputPath)).contains(
+				"META-INF/native-image/reflect-config.json",
+				"META-INF/native-image/resource-config.json",
+				"META-INF/native-image/proxy-config.json");
+	}
+
+	private static List<String> findFiles(Path outputPath) throws IOException {
+		int lengthOfOutputPath = outputPath.toFile().getAbsolutePath().length() + 1;
+		return Files.find(outputPath, Integer.MAX_VALUE,
+					(path, attributes) -> attributes.isRegularFile())
+				.map(Path::toAbsolutePath)
+				.map(Path::toString)
+				.map(path -> path.substring(lengthOfOutputPath))
+				.toList();
+	}
+
+}