How can I mock a validation provider in Cakephp - cakephp

Question

I have a validator that checks if a vat-number is correct. In order to do that it calls an external service. This external call slows the tests down and is unreliable, so I would like to mock it, but I don't understand how I could do it.
public function validationDefault(Validator $validator)
{
$validator->setProvider('vat', 'App\Model\Validation\VatValidation');
$validator->add('vat_no', 'isValidVatNo', [
'rule' => 'validVatNumber',
'provider' => 'vat',
]);
}
And this is the validation provider:
<?php
namespace App\Model\Validation;
use Cake\Core\Configure;
use Cake\Validation\Validation;
use VatNumberCheck\Utility\Model\VatNumberCheck;
class VatValidation extends Validation
{
public static function validVatNumber($check)
{
$vatNumberCheck = new VatNumberCheck();
try {
return $vatNumberCheck->check($check);
} catch (InternalErrorException $e) {
return false;
}
}
}

Answer 1

public function testValidationFail() {
$VatValidator = $this->getMockBuilder('Cake\Validation\Validator')
->setMethods(['validVatNumber'])
->getMock();
$VatValidator->expects($this->any())
->method('validVatNumber')
->will($this->returnValue(false));
$this->Users->getValidator()->setProvider('vat', $VatValidator);
$user = $this->Users->newEntity([
'vat_no' => 'asdf',
]);
$errors = $user->errors();
$this->assertArrayHasKey('vat_no', $errors);
}