How is testing the registry pattern or singleton hard in PHP?

Question

Why is testing singletons or registry pattern hard in a language like PHP which is request driven?

You can write and run tests aside from the actual program executio

Answer 1

When finishing a PHP test, you can flush singleton instance like this:

protected function tearDown()
{
    $reflection = new ReflectionClass('MySingleton');
    $property = $reflection->getProperty("_instance");
    $property->setAccessible(true);
    $property->setValue(null);
}