Convert internal-class-loader tests from groovy to java (#12983)

Co-authored-by: Lauri Tulmin <[email protected]>

instrumentation/internal/internal-class-loader/javaagent-integration-tests/src/test/java/io/opentelemetry/javaagent/instrumentation/internal/classloader/RegressionTest.java

@@ -0,0 +1,24 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.javaagent.instrumentation.internal.classloader;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class RegressionTest {
+  // https://github.com/open-telemetry/opentelemetry-java-instrumentation/issues/5155
+  // loading a class that is extended/implemented by a helper class causes
+  // java.lang.LinkageError: loader 'app' (instance of
+  // jdk.internal.loader.ClassLoaders$AppClassLoader)
+  // attempted duplicate interface definition for org.apache.commons.lang3.function.FailableCallable
+  // this test verifies that the duplicate class definition LinkageError is not thrown into
+  // application code
+  @Test
+  void noDuplicateClassDefinition() throws ClassNotFoundException {
+    assertThat(Class.forName("org.apache.commons.lang3.function.FailableCallable")).isNotNull();
+  }
+}

instrumentation/internal/internal-class-loader/javaagent-integration-tests/src/test/java/io/opentelemetry/javaagent/instrumentation/internal/classloader/ResourceInjectionTest.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.javaagent.instrumentation.internal.classloader;
+
+import static io.opentelemetry.instrumentation.test.utils.GcUtils.awaitGc;
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.lang.ref.WeakReference;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.nio.charset.StandardCharsets;
+import java.time.Duration;
+import java.util.Collections;
+import java.util.Enumeration;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicReference;
+import org.apache.commons.lang3.SystemUtils;
+import org.junit.jupiter.api.Test;
+
+class ResourceInjectionTest {
+
+  private static String readLine(URL url) throws Exception {
+    try (BufferedReader reader =
+        new BufferedReader(new InputStreamReader(url.openStream(), StandardCharsets.UTF_8))) {
+      return reader.readLine().trim();
+    }
+  }
+
+  @Test
+  @SuppressWarnings("UnnecessaryAsync")
+  void resourcesInjectedToNonDelegatingClassLoader() throws Exception {
+    String resourceName = "test-resources/test-resource.txt";
+    URL[] urls = {SystemUtils.class.getProtectionDomain().getCodeSource().getLocation()};
+    AtomicReference<URLClassLoader> emptyLoader =
+        new AtomicReference<>(new URLClassLoader(urls, null));
+
+    Enumeration<URL> resourceUrls = emptyLoader.get().getResources(resourceName);
+    assertThat(resourceUrls.hasMoreElements()).isFalse();
+    resourceUrls = null;
+
+    URLClassLoader notInjectedLoader = new URLClassLoader(urls, null);
+
+    // this triggers resource injection
+    emptyLoader.get().loadClass(SystemUtils.class.getName());
+
+    List<URL> resourceList = Collections.list(emptyLoader.get().getResources(resourceName));
+
+    assertThat(resourceList.size()).isEqualTo(2);
+    assertThat(readLine(resourceList.get(0))).isEqualTo("Hello world!");
+    assertThat(readLine(resourceList.get(1))).isEqualTo("Hello there");
+
+    assertThat(notInjectedLoader.getResources(resourceName).hasMoreElements()).isFalse();
+
+    // references to emptyloader are gone
+    emptyLoader.get().close(); // cleanup
+    WeakReference<URLClassLoader> ref = new WeakReference<>(emptyLoader.get());
+    emptyLoader.set(null);
+
+    awaitGc(ref, Duration.ofSeconds(10));
+
+    assertThat(ref.get()).isNull();
+  }
+}