code: def _validate_install(self):
  
          ''' a method to validate heroku is installed '''
  
          self.printer('Checking heroku installation ... ', flush=True)
      
      # import dependencies
          from os import devnull
          from subprocess import call, check_output
          
      # validate cli installation
          sys_command = 'heroku --version'
          try:
              call(sys_command, shell=True, stdout=open(devnull, 'wb'))
          except Exception as err:
              self.printer('ERROR')
              raise Exception('"heroku cli" not installed. GoTo: https://devcenter.heroku.com/articles/heroku-cli')
      
      # print response and return
          self.printer('done.')
          
          return Truf _validate_install(self):
  
          ''' a method to validate heroku is installed '''
  
          self.printer('Checking heroku installation ... ', flush=True)
      
      # import dependencies
          from os import devnull
          from subprocess import call, check_output
          
      # validate cli installation
          sys_command = 'heroku --version'
          try:
              call(sys_command, shell=True, stdout=open(devnull, 'wb'))
          except Exception as err:
              self.printer('ERROR')
              raise Exception('"heroku cli" not installed. GoTo: https://devcenter.heroku.com/articles/heroku-cli')
      
      # print response and return
          self.printer('done.')
          
          return True
docs: a method to validate heroku is installed