How to use the @lumino/messaging.Message function in @lumino/messaging

it('should be called for a message to a tracked widget', () => {
        const content = new Widget();
        const widget = new DocumentWidget({ content, context });

        manager.adoptWidget(context, widget);
        MessageLoop.sendMessage(widget, new Message('foo'));
        expect(manager.methods).to.contain('messageHook');
      });

it('should return false for close-request messages', () => {
        const widget = manager.createWidget(widgetFactory, context);
        const msg = new Message('close-request');

        expect(manager.messageHook(widget, msg)).to.equal(false);
      });

/**
   * A collection of stateless messages related to widgets.
   */
  export
  namespace Msg {
    /**
     * A singleton `'before-show'` message.
     *
     * #### Notes
     * This message is sent to a widget before it becomes visible.
     *
     * This message is **not** sent when the widget is being attached.
     */
    export
    const BeforeShow = new Message('before-show');

    /**
     * A singleton `'after-show'` message.
     *
     * #### Notes
     * This message is sent to a widget after it becomes visible.
     *
     * This message is **not** sent when the widget is being attached.
     */
    export
    const AfterShow = new Message('after-show');

    /**
     * A singleton `'before-hide'` message.
     *
     * #### Notes

*
     * This message is **not** sent when the widget is being attached.
     */
    export
    const BeforeShow = new Message('before-show');

    /**
     * A singleton `'after-show'` message.
     *
     * #### Notes
     * This message is sent to a widget after it becomes visible.
     *
     * This message is **not** sent when the widget is being attached.
     */
    export
    const AfterShow = new Message('after-show');

    /**
     * A singleton `'before-hide'` message.
     *
     * #### Notes
     * This message is sent to a widget before it becomes not-visible.
     *
     * This message is **not** sent when the widget is being detached.
     */
    export
    const BeforeHide = new Message('before-hide');

    /**
     * A singleton `'after-hide'` message.
     *
     * #### Notes

*
     * This message is **not** sent when the widget is being attached.
     */
    export
    const AfterShow = new Message('after-show');

    /**
     * A singleton `'before-hide'` message.
     *
     * #### Notes
     * This message is sent to a widget before it becomes not-visible.
     *
     * This message is **not** sent when the widget is being detached.
     */
    export
    const BeforeHide = new Message('before-hide');

    /**
     * A singleton `'after-hide'` message.
     *
     * #### Notes
     * This message is sent to a widget after it becomes not-visible.
     *
     * This message is **not** sent when the widget is being detached.
     */
    export
    const AfterHide = new Message('after-hide');

    /**
     * A singleton `'before-attach'` message.
     *
     * #### Notes

* A singleton `'after-attach'` message.
     *
     * #### Notes
     * This message is sent to a widget after it is attached.
     */
    export
    const AfterAttach = new Message('after-attach');

    /**
     * A singleton `'before-detach'` message.
     *
     * #### Notes
     * This message is sent to a widget before it is detached.
     */
    export
    const BeforeDetach = new Message('before-detach');

    /**
     * A singleton `'after-detach'` message.
     *
     * #### Notes
     * This message is sent to a widget after it is detached.
     */
    export
    const AfterDetach = new Message('after-detach');

    /**
     * A singleton `'parent-changed'` message.
     *
     * #### Notes
     * This message is sent to a widget when its parent has changed.
     */

* A singleton `'after-detach'` message.
     *
     * #### Notes
     * This message is sent to a widget after it is detached.
     */
    export
    const AfterDetach = new Message('after-detach');

    /**
     * A singleton `'parent-changed'` message.
     *
     * #### Notes
     * This message is sent to a widget when its parent has changed.
     */
    export
    const ParentChanged = new Message('parent-changed');

    /**
     * A singleton conflatable `'update-request'` message.
     *
     * #### Notes
     * This message can be dispatched to supporting widgets in order to
     * update their content based on the current widget state. Not all
     * widgets will respond to messages of this type.
     *
     * For widgets with a layout, this message will inform the layout to
     * update the position and size of its child widgets.
     */
    export
    const UpdateRequest = new ConflatableMessage('update-request');

    /**

* A singleton `'before-attach'` message.
     *
     * #### Notes
     * This message is sent to a widget before it is attached.
     */
    export
    const BeforeAttach = new Message('before-attach');

    /**
     * A singleton `'after-attach'` message.
     *
     * #### Notes
     * This message is sent to a widget after it is attached.
     */
    export
    const AfterAttach = new Message('after-attach');

    /**
     * A singleton `'before-detach'` message.
     *
     * #### Notes
     * This message is sent to a widget before it is detached.
     */
    export
    const BeforeDetach = new Message('before-detach');

    /**
     * A singleton `'after-detach'` message.
     *
     * #### Notes
     * This message is sent to a widget after it is detached.
     */

* #### Notes
     * This message is sent to a widget after it becomes not-visible.
     *
     * This message is **not** sent when the widget is being detached.
     */
    export
    const AfterHide = new Message('after-hide');

    /**
     * A singleton `'before-attach'` message.
     *
     * #### Notes
     * This message is sent to a widget before it is attached.
     */
    export
    const BeforeAttach = new Message('before-attach');

    /**
     * A singleton `'after-attach'` message.
     *
     * #### Notes
     * This message is sent to a widget after it is attached.
     */
    export
    const AfterAttach = new Message('after-attach');

    /**
     * A singleton `'before-detach'` message.
     *
     * #### Notes
     * This message is sent to a widget before it is detached.
     */

* A singleton `'before-detach'` message.
     *
     * #### Notes
     * This message is sent to a widget before it is detached.
     */
    export
    const BeforeDetach = new Message('before-detach');

    /**
     * A singleton `'after-detach'` message.
     *
     * #### Notes
     * This message is sent to a widget after it is detached.
     */
    export
    const AfterDetach = new Message('after-detach');

    /**
     * A singleton `'parent-changed'` message.
     *
     * #### Notes
     * This message is sent to a widget when its parent has changed.
     */
    export
    const ParentChanged = new Message('parent-changed');

    /**
     * A singleton conflatable `'update-request'` message.
     *
     * #### Notes
     * This message can be dispatched to supporting widgets in order to
     * update their content based on the current widget state. Not all