Quick and dirty way to test if an observer responds to a given event in Magento 1 using MageTest

event_dispatch_check.php

<?php

class SomeTestTest extends MageTest_PHPUnit_Framework_TestCase 
{
    /**
     * @param string $observerName e.g. mymodulens_mymodule_does_something_on_order_place
     * @param string $eventName e.g. a dispatched event e.g. sales_order_place_after
     * @param string $area e.g. global/frontend/admin/adminhtml
     */
    public function assertObserverReceivesEvent($observerName, $eventName, $area)
    {
        Mage::app()->getConfig()->whitelistObserver($observerName);
        $config = Mage::app()->getConfig();

        $eventConfig = $config->getEventConfig($area, $eventName);

        if (isset($eventConfig->observers->$observerName)) {
            $observer = $eventConfig->observers->$observerName;
            $class = (string)$observer->class;
            $mock = $this->getModelMock($class);
            $mock->expects($this->once())
                ->method((string)$observer->method);

            $config->setModelInstanceMock($class, $mock);
            Mage::dispatchEvent($eventName, array());
        } else {
            $this->fail('No observer called ' . $observerName . ' is listening for event ' . $eventName . ' in area ' . $area);
        }
    }
}