test__api.py: update test for spawn_later

greentest/test__api.py

@@ -53,11 +53,14 @@ class Test(greentest.TestCase):
     def test_killing_not_yet_started(self):
         def func():
             pass
-        g = gevent.spawn_later(2000, func)
-        assert not g.dead, g
-        g.kill(block=True)
-        assert g.dead, g
-        self.assertRaises(Exception, g.get)
+        g, timer = gevent.spawn_later(2000, func)
+        try:
+            assert not g.dead, g
+            g.kill(block=True)
+            assert g.dead, g
+            self.assertRaises(Exception, g.get)
+        finally:
+            timer.cancel()
 
     def test_sleep_invalid_switch(self):
         p = gevent.spawn(util.wrap_errors(AssertionError, gevent.sleep), 2)