Remove AgentTestRunner custom classloader.

BytebuddyAgent install already handles class retransformation, make
the custom classloader redundant.

dd-java-agent/testing/src/main/java/dd/test/AgentTestRunner.java

@@ -4,19 +4,12 @@ import com.datadoghq.agent.AgentInstaller;
 import com.datadoghq.trace.DDTracer;
 import com.datadoghq.trace.writer.ListWriter;
 import io.opentracing.Tracer;
-import java.io.IOException;
 import java.lang.instrument.ClassFileTransformer;
 import java.lang.instrument.Instrumentation;
-import java.lang.reflect.Field;
 import net.bytebuddy.agent.ByteBuddyAgent;
-import net.bytebuddy.dynamic.ClassFileLocator;
 import org.junit.AfterClass;
 import org.junit.Before;
 import org.junit.BeforeClass;
-import org.junit.runner.RunWith;
-import org.junit.runner.notification.RunNotifier;
-import org.junit.runners.model.InitializationError;
-import org.spockframework.runtime.Sputnik;
 import org.spockframework.runtime.model.SpecMetadata;
 import spock.lang.Specification;
 
@@ -35,7 +28,6 @@ import spock.lang.Specification;
  *       in an initialized state.
  * </ul>
  */
-@RunWith(AgentTestRunner.SpockRunner.class)
 @SpecMetadata(filename = "AgentTestRunner.java", line = 0)
 public abstract class AgentTestRunner extends Specification {
   /**
@@ -75,76 +67,4 @@ public abstract class AgentTestRunner extends Specification {
     instrumentation.removeTransformer(activeTransformer);
     activeTransformer = null;
   }
-
-  // FIXME: Remove SpockRunner and custom classload logic
-
-  public static class SpockRunner extends Sputnik {
-    private final InstrumentationClassLoader customLoader;
-
-    public SpockRunner(Class<?> clazz)
-        throws InitializationError, NoSuchFieldException, SecurityException,
-            IllegalArgumentException, IllegalAccessException {
-      super(shadowTestClass(clazz));
-      // access the classloader created in shadowTestClass above
-      Field clazzField = Sputnik.class.getDeclaredField("clazz");
-      try {
-        clazzField.setAccessible(true);
-        customLoader =
-            (InstrumentationClassLoader) ((Class<?>) clazzField.get(this)).getClassLoader();
-      } finally {
-        clazzField.setAccessible(false);
-      }
-    }
-
-    // Shadow the test class with bytes loaded by InstrumentationClassLoader
-    private static Class<?> shadowTestClass(final Class<?> clazz) {
-      try {
-        InstrumentationClassLoader customLoader =
-            new InstrumentationClassLoader(SpockRunner.class.getClassLoader());
-        return customLoader.shadow(clazz);
-      } catch (IOException e) {
-        throw new IllegalStateException(e);
-      }
-    }
-
-    // Replace the context class loader for each test with InstrumentationClassLoader
-    @Override
-    public void run(final RunNotifier notifier) {
-      final ClassLoader contextLoader = Thread.currentThread().getContextClassLoader();
-      try {
-        Thread.currentThread().setContextClassLoader(customLoader);
-        super.run(notifier);
-      } finally {
-        Thread.currentThread().setContextClassLoader(contextLoader);
-      }
-    }
-  }
-
-  /**
-   * A ClassLoader which retransforms classes unseen by the installed agent. With the exception of
-   * shadowed classes, this class
-   */
-  private static class InstrumentationClassLoader extends java.lang.ClassLoader {
-    final ClassLoader parent;
-
-    public InstrumentationClassLoader(ClassLoader parent) {
-      super(parent);
-      this.parent = parent;
-    }
-
-    /** Forcefully inject the bytes of clazz into this classloader. */
-    public Class<?> shadow(Class<?> clazz) throws IOException {
-      final ClassFileLocator locator = ClassFileLocator.ForClassLoader.of(clazz.getClassLoader());
-      final byte[] classBytes = locator.locate(clazz.getName()).resolve();
-
-      Class<?> shadowed = this.defineClass(clazz.getName(), classBytes, 0, classBytes.length);
-      return shadowed;
-    }
-
-    @Override
-    protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
-      // TODO: If already loaded and not seen by agent: do a retransform.
-      return parent.loadClass(name);
-    }
-  }
 }