FunctionalTest::testPing PHP Method

    public function testPing()
    {
        $client = $this->client;
        $promise = $client->ping();
        $this->assertInstanceOf('React\\Promise\\PromiseInterface', $promise);
        $promise->then($this->expectCallableOnce('PONG'));
        $this->assertTrue($client->isBusy());
        $this->waitFor($client);
        $this->assertFalse($client->isBusy());
        return $client;
    }