Add shading test

Author: trask

javaagent/src/test/java/io/opentelemetry/javaagent/ShadingTest.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.javaagent;
+
+import static java.util.Arrays.asList;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.File;
+import java.lang.management.ManagementFactory;
+import java.lang.management.RuntimeMXBean;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
+import org.junit.jupiter.api.Test;
+
+class ShadingTest {
+
+  private static final List<String> EXPECTED_ENTRY_PREFIXES =
+      asList("io/opentelemetry/javaagent/", "inst/", "META-INF/");
+
+  @Test
+  void agentJarContainsOnlyExpectedEntries() throws Exception {
+    String agentJarPath = getAgentJarPath();
+    assertThat(agentJarPath).isNotNull();
+
+    File agentJar = new File(agentJarPath);
+    assertThat(agentJar).exists();
+    assertThat(agentJar).isFile();
+
+    List<String> unexpectedEntries = new ArrayList<>();
+
+    try (JarFile jarFile = new JarFile(agentJar)) {
+      jarFile.stream()
+          .map(JarEntry::getName)
+          .filter(entryName -> !entryName.endsWith("/")) // Skip directories
+          .forEach(
+              entryName -> {
+                boolean isExpected =
+                    EXPECTED_ENTRY_PREFIXES.stream().anyMatch(entryName::startsWith);
+                if (!isExpected) {
+                  unexpectedEntries.add(entryName);
+                }
+              });
+    }
+
+    assertThat(unexpectedEntries)
+        .as(
+            "Agent jar should only contain entries with expected prefixes: %s",
+            EXPECTED_ENTRY_PREFIXES)
+        .isEmpty();
+  }
+
+  private static String getAgentJarPath() {
+    RuntimeMXBean runtimeMxBean = ManagementFactory.getRuntimeMXBean();
+    for (String arg : runtimeMxBean.getInputArguments()) {
+      if (arg.startsWith("-javaagent:")) {
+        return arg.substring("-javaagent:".length());
+      }
+    }
+    return null;
+  }
+}