fix(testing): reset collected statuses in Harness.evaluate_status (#1048

)

This addresses #736 (comment)

ops/charm.py

@@ -865,7 +865,7 @@ class CollectStatusEvent(EventBase):
 
     The framework will trigger these events after the hook code runs
     successfully (``collect_app_status`` will only be triggered on the leader
-    unit). If any statuses were added by the event handlers using
+    unit). If any statuses were added by the event handler using
     :meth:`add_status`, the framework will choose the highest-priority status
     and set that as the status (application status for ``collect_app_status``,
     or unit status for ``collect_unit_status``).

ops/testing.py

@@ -1633,7 +1633,12 @@ def evaluate_status(self) -> None:
 
         Tests should normally call this and then assert that ``self.model.app.status``
         or ``self.model.unit.status`` is the value expected.
+
+        Evaluation is not "additive"; this method resets the added statuses before
+        triggering each collect-status event.
         """
+        self.charm.app._collected_statuses = []
+        self.charm.unit._collected_statuses = []
         charm._evaluate_status(self.charm)
 
     def handle_exec(self,

test/test_testing.py

@@ -2828,20 +2828,28 @@ def __init__(self, framework: ops.Framework):
                 super().__init__(framework)
                 self.framework.observe(self.on.collect_app_status, self._on_collect_app_status)
                 self.framework.observe(self.on.collect_unit_status, self._on_collect_unit_status)
+                self.app_status_to_add = ops.BlockedStatus('blocked app')
+                self.unit_status_to_add = ops.BlockedStatus('blocked unit')
 
             def _on_collect_app_status(self, event: ops.CollectStatusEvent):
-                event.add_status(ops.ActiveStatus())
+                event.add_status(self.app_status_to_add)
 
             def _on_collect_unit_status(self, event: ops.CollectStatusEvent):
-                event.add_status(ops.BlockedStatus('bar'))
+                event.add_status(self.unit_status_to_add)
 
         harness = ops.testing.Harness(TestCharm)
         harness.set_leader(True)
         harness.begin()
         # Tests for the behaviour of status evaluation are in test_charm.py
         harness.evaluate_status()
-        self.assertEqual(harness.model.app.status, ops.ActiveStatus())
-        self.assertEqual(harness.model.unit.status, ops.BlockedStatus('bar'))
+        self.assertEqual(harness.model.app.status, ops.BlockedStatus('blocked app'))
+        self.assertEqual(harness.model.unit.status, ops.BlockedStatus('blocked unit'))
+
+        harness.charm.app_status_to_add = ops.ActiveStatus('active app')
+        harness.charm.unit_status_to_add = ops.ActiveStatus('active unit')
+        harness.evaluate_status()
+        self.assertEqual(harness.model.app.status, ops.ActiveStatus('active app'))
+        self.assertEqual(harness.model.unit.status, ops.ActiveStatus('active unit'))
 
 
 class TestNetwork(unittest.TestCase):