const joi = require('joi');
const ourJoi = joi.extend({
    base: joi.string(),
    name: 'string',
    language: {
        // Note: Missing translation here!
    },
    rules: [
        {
            name: 'something',
            validate (params, value, state, options) {
                if (value !== '0') {
                    return this.createError('string.something', {
                        v: value,
                    }, state, options);
                }
                return value;
            },
        },
    ],
});

ourJoi.validate('test', ourJoi.string().something()); // <<<< Error Here