code: def assertFileExists(self, filename, msg=None):
          '''Fail if ``filename`` does not exist as determined by
          ``os.path.isfile(filename)``.
  
          Parameters
          ----------
          filename : str, bytes
          msg : str
              If not provided, the :mod:`marbles.mixins` or
              :mod:`unittest` standard message will be used.
          '''
          standardMsg = '%s does not exist' % filename
  
          if not os.path.isfile(filename):
              self.fail(self._formatMessage(msg, standardMsg)f assertFileExists(self, filename, msg=None):
          '''Fail if ``filename`` does not exist as determined by
          ``os.path.isfile(filename)``.
  
          Parameters
          ----------
          filename : str, bytes
          msg : str
              If not provided, the :mod:`marbles.mixins` or
              :mod:`unittest` standard message will be used.
          '''
          standardMsg = '%s does not exist' % filename
  
          if not os.path.isfile(filename):
              self.fail(self._formatMessage(msg, standardMsg))
docs: Fail if ``filename`` does not exist as determined by
          ``os.path.isfile(filename)``.
  
          Parameters
          ----------
          filename : str, bytes
          msg : str
              If not provided, the :mod:`marbles.mixins` or
              :mod:`unittest` standard message will be used.