ValidateSometimes.php

<?php
namespace App\Http\Requests;

use Illuminate\Foundation\Http\FormRequest;

class SomeRequest extends FormRequest
{
    /**
     * Validate conditional rules.
     *
     * @return \Illuminate\Contracts\Validation\Validator
     */
    protected function getValidatorInstance()
    {
        $validator = parent::getValidatorInstance();

        $validator->sometimes('g-recaptcha-response', 'required|captcha', function ($input) {
            return ! app()->environment('testing');
        });

        return $validator;
    }
}