Braintree\SubscriptionSearch::transactionId PHP Method

    public static function transactionId()
    {
        return new TextNode('transaction_id');
    }

 public function testSearch_transactionId()
 {
     $creditCard = SubscriptionHelper::createCreditCard();
     $triallessPlan = SubscriptionHelper::triallessPlan();
     $matchingSubscription = Braintree\Subscription::create(['paymentMethodToken' => $creditCard->token, 'planId' => $triallessPlan['id']])->subscription;
     $nonMatchingSubscription = Braintree\Subscription::create(['paymentMethodToken' => $creditCard->token, 'planId' => $triallessPlan['id']])->subscription;
     $collection = Braintree\Subscription::search([Braintree\SubscriptionSearch::transactionId()->is($matchingSubscription->transactions[0]->id)]);
     $this->assertTrue(Test\Helper::includes($collection, $matchingSubscription));
     $this->assertFalse(Test\Helper::includes($collection, $nonMatchingSubscription));
 }