ATO-218 Always set slot values

This fixes a bug where slot values vanish when using the augmented
memoization policy. If in the past, the slot is set to a specific value,
and then later the slot being set to the same value, no new SlotSet
event is emitted. However, this leads to the augmented memoiziation
policy wrongly assuming this slot to be unset, as the older, original
SlotSet event was pruned already.

rasa/core/actions/action.py

@@ -1225,8 +1225,7 @@ async def run(
                     if not isinstance(slot, ListSlot):
                         value = value[-1]
 
-                    if tracker.get_slot(slot.name) != value:
-                        slot_events.append(SlotSet(slot.name, value))
+                    slot_events.append(SlotSet(slot.name, value))
 
                 should_fill_custom_slot = mapping_type == SlotMappingType.CUSTOM
 

tests/core/actions/test_extract_slots.py

@@ -0,0 +1,56 @@
+import textwrap
+from unittest.mock import Mock
+
+from rasa.core.actions.action import ActionExtractSlots
+from rasa.core.channels import CollectingOutputChannel
+from rasa.shared.core.domain import Domain
+from rasa.shared.core.events import UserUttered, SlotSet
+from rasa.shared.core.trackers import DialogueStateTracker
+
+
+async def test_action_extract_slots_returns_slot_set_even_if_slot_value_is_unchanged():
+    event_with_slot_entity = UserUttered(
+        text="I am a text",
+        intent={"name": "intent_with_entity"},
+        entities=[{"entity": "entity", "value": "value"}],
+    )
+
+    domain = textwrap.dedent(
+        """
+          intents:
+            - intent_with_entity
+          entities:
+            - entity
+          slots:
+            entity:
+              type: text
+              mappings:
+              - type: from_entity
+                entity: entity
+        """
+    )
+
+    domain = Domain.from_yaml(domain)
+
+    tracker = DialogueStateTracker.from_events(
+        "some-sender",
+        evts=[
+            event_with_slot_entity,
+        ],
+    )
+
+    tracker._set_slot("entity", "value")
+
+    action = ActionExtractSlots(None)
+
+    events = await action.run(
+        output_channel=CollectingOutputChannel(),
+        nlg=Mock(),
+        tracker=tracker,
+        domain=domain,
+    )
+
+    assert len(events) == 1
+    assert type(events[0]) == SlotSet
+    assert events[0].key == "entity"
+    assert events[0].value == "value"