Fix failing test (#3269)

examples/distro/gradle/instrumentation.gradle

@@ -38,6 +38,8 @@ shadowJar {
 }
 
 tasks.withType(Test).configureEach {
+  inputs.file(shadowJar.archiveFile)
+
   jvmArgs "-Dotel.javaagent.debug=true"
   jvmArgs "-javaagent:${configurations.testAgent.files.first().absolutePath}"
   jvmArgs "-Dotel.javaagent.experimental.initializer.jar=${shadowJar.archiveFile.get().asFile.absolutePath}"

javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/ExtensionClassLoader.java

@@ -44,6 +44,10 @@ public class ExtensionClassLoader extends URLClassLoader {
                 System.getenv("OTEL_JAVAAGENT_EXPERIMENTAL_INITIALIZER_JAR"))));
     // TODO when logging is configured add warning about deprecated property
 
+    if (extension.isEmpty()) {
+      return parent;
+    }
+
     List<ClassLoader> delegates = new ArrayList<>(extension.size());
     for (URL url : extension) {
       delegates.add(getDelegate(parent, url));

javaagent/javaagent.gradle

@@ -133,6 +133,8 @@ dependencies {
 }
 
 tasks.withType(Test).configureEach {
+  inputs.file(shadowJar.archiveFile)
+
   jvmArgs "-Dotel.javaagent.debug=true"
 
   doFirst {

testing/agent-for-testing/agent-for-testing.gradle

@@ -88,6 +88,8 @@ dependencies {
 
 afterEvaluate {
   tasks.withType(Test).configureEach {
+    inputs.file(shadowJar.archiveFile)
+
     jvmArgs "-Dotel.javaagent.debug=true"
     jvmArgs "-javaagent:${shadowJar.archiveFile.get().asFile.absolutePath}"