discard async cleanups when running them

src/twisted/trial/_asynctest.py

@@ -199,7 +199,8 @@ def deferRunCleanups(self, ignored, result):
         object.
         """
         failures = []
-        for func, args, kwargs in self._cleanups[::-1]:
+        while len(self._cleanups) > 0:
+            func, args, kwargs = self._cleanups.pop()
             try:
                 yield func(*args, **kwargs)
             except Exception:

src/twisted/trial/newsfragments/10320.bugfix

@@ -0,0 +1,2 @@
+
+twisted.trial.unittest.TestCase now discards cleanup functions after running them.  Notably, this prevents them from being run an ever growing number of times with `trial -u ...`.

src/twisted/trial/test/test_tests.py

@@ -962,6 +962,21 @@ def test_multipleErrorsReported(self):
         self.assertEqual(error1.getErrorMessage(), "bar")
         self.assertEqual(error2.getErrorMessage(), "foo")
 
+    def test_cleanupRunsOnce(self):
+        """
+        A function registered as a cleanup is run once.
+        """
+        cleanups = []
+        self.test.addCleanup(lambda: cleanups.append(stage))
+        # It should get run this time.
+        stage = "first"
+        self.test.run(self.result)
+        # It should not get run the next time since it has not been
+        # re-registered.
+        stage = "second"
+        self.test.run(self.result)
+        self.assertEqual(cleanups, ["first"])
+
 
 class SynchronousAddCleanupTests(AddCleanupMixin, unittest.SynchronousTestCase):
     """