Testing Cashier using mocks

I've worked out how to create a token, and from there run tests against Cashier, but I'm not using Mocks so they take quite a while to run.

I create a token like this:

private function createToken($cardNum)
    {
        \Stripe\Stripe::setApiKey(env('STRIPE_SECRET'));
        $data = \Stripe\Token::create([
            'card' => [
                "number" => $cardNum,
                "exp_month" => 11,
                "exp_year" => 2036,
                "cvc" => "314"
            ]
        ]);

        return $data['id'];
    }

Then I can create a new subscription like this:

$token = $this->createToken('4242424242424242');
$this->user->createAsStripeCustomer($token);
$this->user->newSubscription('default', 'standard')->create();

Would anyone know how I could use mocking so I don't hit the Stripe API to speed up these tests?