Google\Cloud\PubSub\Topic::subscription PHP Method

    public function subscription($name)
    {
        return $this->subscriptionFactory($name);
    }

 public function testSubscription()
 {
     $topic = new Topic($this->connection->reveal(), 'topic-name', 'project-name');
     $subscription = $topic->subscription('subscription-name');
     $this->assertInstanceOf(Subscription::class, $subscription);
 }