How To Mock Functions Without Class in laravel?

I have a Function Which is loaded by composer autoload

    "autoload": {
        "files": [
            "app/Helpers/SmsHelper.php",
        ]
    },

This File Has a smsHelper Function Which Can send SMS. One Of My class is use this Helper and i want to write test for this class. could some one tell me how to mock this function? because i don't want to send SMS in testing mode

via Chebli Mohamed