public class E4SWTBot extends SWTBot(){

  private IEclipseContext serviceContext;
  private IEclipseContext context;

  public E4SWTBot(){
    serviceContext = E4Workbench.getServiceContext();
  }

  public EPartService getPartService(){
    context = serviceContext.getActiveLeaf();
    return context.get(EPartService.class);
  }

  public void selectPart(String partId){
    Display.getDefault().asyncExec(new Runnable(){
      public void run(){
        // get the part 
        MPart part = getPartService().findPart( partId );
        // Here your code to interact with part
        getPartService.activate(part);
      }
    });
  }

}