code: function validation() {
    const target = this._obj;
    this.assert(_.isObject(target), '#{this} is not a Joi validation because it must be an object');
    this.assert(!_.isEmpty(target), '#{this} is not a Joi validation because it is an empty object');
    const fields = _.keys(target);
    const allFieldsPresent = _.every(FIELDS_TO_VALIDATE.map(field => _.includes(fields, field)));
  
    this.assert(
      allFieldsPresent,
      `${this} is not a validation because it does not contain expected keys`
    );
  }
docs: Assert that target is a Joi validation
  @example
  expect(target).to.[not].be.a.validation
  target.should.[not].be.a.validation