code: function assert (assertValue, message, err) {
      if (!assertValue) {
          throw defined(this) ? this.error(message, err) : error(message, err)
      }
  }
docs: @function assert
  
  throw error if value is not true
  
  @param {boolean} assertValue
  @param {string} message
  @param {Error|undefined} error
  
  @throws {Error}