Protobuf\Configuration::getExtensionRegistry PHP Method

    public function getExtensionRegistry()
    {
        if ($this->extensionRegistry === null) {
            $this->extensionRegistry = new ExtensionRegistry();
        }
        return $this->extensionRegistry;
    }

 public function testGetAndSetExtensionRegistry()
 {
     $mock = $this->getMock('Protobuf\\Extension\\ExtensionRegistry');
     $registry = $this->configuration->getExtensionRegistry();
     $this->assertInstanceOf('Protobuf\\Extension\\ExtensionRegistry', $registry);
     $this->assertSame($registry, $this->configuration->getExtensionRegistry());
     $this->configuration->setExtensionRegistry($mock);
     $this->assertSame($mock, $this->configuration->getExtensionRegistry());
 }