I'm trying to migrate a bunch of tests from SimpleTest to PHPUnit and I was wondering if there is an equivalent for SimpleTest's partial mocks.
Update: I can't seem to find anything in the docs which suggests that this feature is available, but it occurred to me that I could just use a subclass. Is this a good or bad idea?
class StuffDoer {
    protected function doesLongRunningThing() {
        sleep(10);
        return "stuff";
    }
    public function doStuff() {
        return $this->doesLongRunningThing();
    }
}
class StuffDoerTest {
    protected function doesLongRunningThing() {
        return "test stuff";
    }
}
class StuffDoerTestCase extends PHPUnit_Framework_TestCase {
    public function testStuffDoer() {
        $sd = new StuffDoerTest();
        $result = $sd->doStuff();
        $this->assertEquals($result, "test stuff");
    }
}