import java.util.concurrent.CopyOnWriteArraySet;
import org.jspecify.annotations.Nullable;

/**
 * Registry of subscribers to a single event bus.
 *
 * @author Colin Decker
 */
final class SubscriberRegistry {

  /**
   * All registered subscribers, indexed by event type.
   *
   * <p>The {@link CopyOnWriteArraySet} values make it easy and relatively lightweight to get an

import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;

/**
 * Tests for {@link SubscriberRegistry}.
 *
 * @author Colin Decker
 */
@NullUnmarked
public class SubscriberRegistryTest extends TestCase {

  private final SubscriberRegistry registry = new SubscriberRegistry(new EventBus());

  public void testRegister() {
    assertEquals(0, registry.getSubscribersForTesting(String.class).size());

  private final String identifier;
  private final Executor executor;
  private final SubscriberExceptionHandler exceptionHandler;

  private final SubscriberRegistry subscribers = new SubscriberRegistry(this);
  private final Dispatcher dispatcher;

  /** Creates a new EventBus named "default". */
  public EventBus() {
    this("default");
  }

  /**