text: from django.apps import AppConfig
  from django.core.exceptions import ImproperlyConfigured
  from .tools import mjml_render
  from . import settings as mjml_settings
  
  
  def check_mjml_command():
      try:
          html = mjml_render('<mjml><mj-body><mj-container><mj-text>MJMLv3'
                             '</mj-text></mj-container></mj-body></mjml>')
      except RuntimeError:
          try:
              html = mjml_render('<mjml><mj-body><mj-section><mj-column><mj-text>MJMLv4'
                                 '</mj-text></mj-column></mj-section></mj-body></mjml>')
          except RuntimeError as e:
              raise ImproperlyConfigured(e)
      if '<html ' not in html:
          raise ImproperlyConfigured(
              'mjml command returns wrong result.\n'
              'Check MJML is installed correctly. See https://github.com/mjmlio/mjml#installation'
          )
  
  
  class MJMLConfig(AppConfig):
      name = 'mjml'
      verbose_name = 'Use MJML in Django templates'
  
      def ready(self):
          if mjml_settings.MJML_BACKEND_MODE == 'cmd' and mjml_settings.MJML_CHECK_CMD_ON_STARTUP:
              check_mjml_command()
  