add assert

src/php/tests/unit_tests/CallInvokerTest.php

@@ -176,11 +176,13 @@ class CallInvokerTest extends \PHPUnit\Framework\TestCase
     public function testCreateDefaultCallInvoker()
     {
         $call_invoker = new \Grpc\DefaultCallInvoker();
+        $this->assertNotNull($call_invoker);
     }
 
     public function testCreateCallInvoker()
     {
         $call_invoker = new CallInvokerUpdateChannel();
+        $this->assertNotNull($call_invoker);
     }
 
     public function testCallInvokerAccessChannel()

src/php/tests/unit_tests/ChannelTest.php

@@ -39,8 +39,9 @@ class ChannelTest extends \PHPUnit\Framework\TestCase
 
     public function testConstructorCreateSsl()
     {
-        new Grpc\Channel('localhost:50033', 
+        $channel = new Grpc\Channel('localhost:50033', 
             ['credentials' => \Grpc\ChannelCredentials::createSsl()]);
+        $this->assertNotNull($channel);
     }
 
     public function testGetConnectivityState()