Is it possible to have only 1 implementation of IAnnotationTransformer in a project

Question

Can we have more than 1 implementation of IAnnotationTransformer in a project that is using TestNG? I'm using TestNg version 7.0.0.

Answer 1

TestNG currently lets you wire in ONLY ONE implementation of IAnnotationTransformer. If you try to plug in multiple ones of them, the last one that got added is what will get invoked.

There's an open issue that is tracking this ask. See GITHUB-1894.

As an alternative you can build your own composite IAnnotationTransformer which can be used to iterate through all the other annotation transformer instances. Here's a sample (Its available in the above mentioned github link)

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.List;
import org.testng.IAnnotationTransformer;
import org.testng.annotations.ITestAnnotation;
import org.testng.collections.Lists;
import org.testng.internal.ClassHelper;

public class CompositeTransformer implements IAnnotationTransformer {
  private static final String JVM_ARGS =
      "com.rationaleemotions.github.issue1894.Listener1, com.rationaleemotions.github.issue1894.Listener2";
  private List<IAnnotationTransformer> transformers = Lists.newArrayList();

  public CompositeTransformer() {
    // Ideally this would get a value from the command line. But just for demo purposes
    // I am hard-coding the values.
    String listeners = System.getProperty("transformers", JVM_ARGS);

    Arrays.stream(listeners.split(","))
        .forEach(
            each -> {
              Class<?> clazz = ClassHelper.forName(each.trim());
              IAnnotationTransformer transformer =
                  (IAnnotationTransformer) ClassHelper.newInstance(clazz);
              transformers.add(transformer);
            });
  }

  @Override
  public void transform(
      ITestAnnotation annotation, Class testClass, Constructor testConstructor, Method testMethod) {
    for (IAnnotationTransformer each : transformers) {
      each.transform(annotation, testClass, testConstructor, testMethod);
    }
  }
}