switch (eventType) {
                case ProjectDiscoveryStarted:
                    listener.projectDiscoveryStarted(event);
                    break;

                case SessionStarted:
                    listener.sessionStarted(event);
                    break;
                case SessionEnded:
                    listener.sessionEnded(event);
                    break;

                case ProjectSkipped:

        setMdc(event);
        delegate.projectDiscoveryStarted(event);
    }

    @Override
    public void sessionStarted(ExecutionEvent event) {
        setMdc(event);
        buildEventListener.sessionStarted(event);
        delegate.sessionStarted(event);
    }

    @Override
    public void sessionEnded(ExecutionEvent event) {
        setMdc(event);
        delegate.sessionEnded(event);

        dispatcher.onEvent(event);
        delegate.projectDiscoveryStarted(event);
    }

    @Override
    public void sessionStarted(ExecutionEvent event) {
        dispatcher.onEvent(event);
        delegate.sessionStarted(event);
    }

    @Override
    public void sessionEnded(ExecutionEvent event) {
        dispatcher.onEvent(event);
        delegate.sessionEnded(event);
    }

    @Override
    public void projectDiscoveryStarted(ExecutionEvent event) {
        // default does nothing
    }

    @Override
    public void sessionStarted(ExecutionEvent event) {
        // default does nothing
    }

    @Override
    public void sessionEnded(ExecutionEvent event) {
        // default does nothing
    }

    @Override

import org.apache.maven.execution.ExecutionEvent;
import org.eclipse.aether.transfer.TransferEvent;

/**
 * An abstract build event sink.
 */
public interface BuildEventListener {

    void sessionStarted(ExecutionEvent event);

    void projectStarted(String projectId);

    void projectLogMessage(String projectId, String event);

    void projectFinished(String projectId);

     * Note: do not modify this enum, or, make sure that this enum and
     * {@link org.apache.maven.api.EventType} have same elements in same order.
     */
    enum Type {
        ProjectDiscoveryStarted,
        SessionStarted,
        SessionEnded,
        ProjectSkipped,
        ProjectStarted,
        ProjectSucceeded,
        ProjectFailed,
        MojoSkipped,
        MojoStarted,
        MojoSucceeded,
        MojoFailed,

 * {@link AbstractExecutionListener} in order to avoid interoperability problems.
 *
 */
public interface ExecutionListener {

    void projectDiscoveryStarted(ExecutionEvent event);

    void sessionStarted(ExecutionEvent event);

    void sessionEnded(ExecutionEvent event);

    void projectSkipped(ExecutionEvent event);

    void projectStarted(ExecutionEvent event);

    final Consumer<String> output;

    public SimpleBuildEventListener(Consumer<String> output) {
        this.output = output;
    }

    @Override
    public void sessionStarted(ExecutionEvent event) {}

    @Override
    public void projectStarted(String projectId) {}

    @Override
    public void projectLogMessage(String projectId, String event) {
        log(event);
    }

        ExecutionEvent projectStartedEvent3 = mock(ExecutionEvent.class);
        when(projectStartedEvent3.getProject()).thenReturn(project3);

        // execute
        executionEventLogger.sessionStarted(sessionStartedEvent);
        executionEventLogger.projectStarted(projectStartedEvent1);
        executionEventLogger.projectStarted(projectStartedEvent2);
        executionEventLogger.projectStarted(projectStartedEvent3);

        this.builders = builders;
    }

    @Override
    public void execute(MavenSession session) {
        eventCatapult.fire(ExecutionEvent.Type.SessionStarted, session, null);

        ReactorContext reactorContext = null;
        ProjectBuildList projectBuilds = null;
        MavenExecutionResult result = session.getResult();

        try {