From 83819da7c2aa1878bad7b4b1b3a0cfdac3062aca Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Thu, 1 Oct 2020 15:51:09 +0200
Subject: [PATCH 01/16] FormSlotsValidatorAction added

---
 rasa_sdk/forms.py | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index 84dac4e73..212eacae1 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -691,3 +691,45 @@ def _get_entity_type_of_slot_to_fill(
                 return None
 
         return entity_type
+
+
+class FormSlotsValidatorAction(Action):
+    def name(self) -> Text:
+        """Unique identifier of this action."""
+
+        raise NotImplementedError("An action must implement a name")
+
+    def run(
+        self, dispatcher, tracker: Tracker, domain: Dict
+    ) -> List[EventType]:
+        """Execute the side effects of this action.
+
+        Args:
+            dispatcher: the dispatcher which is used to
+                send messages back to the user. Use
+                ``dispatcher.utter_message()`` for sending messages.
+            tracker: the state tracker for the current
+                user. You can access slot values using
+                ``tracker.get_slot(slot_name)``, the most recent user message
+                is ``tracker.latest_message.text`` and any other
+                ``rasa_sdk.Tracker`` property.
+            domain: the bot's domain
+        Returns:
+            A dictionary of ``rasa_sdk.events.Event`` instances that is
+                returned through the endpoint
+        """
+
+        slots_to_validate: Dict[Text, Any] = tracker.form_slots_to_validate()
+        validation_events = []
+
+        for slot_name, slot_value in slots_to_validate.items():
+            function_name = f"validate_{slot_name}"
+            fn = getattr(self, function_name)
+            if fn(tracker, domain, slot_value):
+                validation_events.append(SlotSet(slot_name, slot_value))
+            else:
+                # Return a `SlotSet` event with value `None` to indicate that this
+                # slot still needs to be filled.
+                validation_events.append(SlotSet(slot_name, None))
+
+        return validation_events

From a8ee5b3548c27956f2bebbdda5ba1ca8fc5a645f Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Fri, 2 Oct 2020 10:24:50 +0200
Subject: [PATCH 02/16] FormSlotsValidatorAction tests

---
 rasa_sdk/forms.py                  | 23 ++++--------
 rasa_sdk/interfaces.py             |  6 +--
 rasa_sdk/knowledge_base/actions.py | 17 +++------
 tests/test_actions.py              | 10 +----
 tests/test_forms.py                | 59 +++++++++++++++++++++++++++++-
 5 files changed, 75 insertions(+), 40 deletions(-)

diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index 212eacae1..f5bfd70e6 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -672,8 +672,7 @@ def __str__(self) -> Text:
         return f"FormAction('{self.name()}')"
 
     def _get_entity_type_of_slot_to_fill(
-        self,
-        slot_to_fill: Optional[Text],
+        self, slot_to_fill: Optional[Text],
     ) -> Optional[Text]:
         if not slot_to_fill:
             return None
@@ -694,29 +693,23 @@ def _get_entity_type_of_slot_to_fill(
 
 
 class FormSlotsValidatorAction(Action):
+    """An action that validates if every extracted slot is valid."""
+
     def name(self) -> Text:
         """Unique identifier of this action."""
 
         raise NotImplementedError("An action must implement a name")
 
-    def run(
-        self, dispatcher, tracker: Tracker, domain: Dict
-    ) -> List[EventType]:
+    async def run(self, dispatcher, tracker: "Tracker", domain: Dict) -> List[EventType]:
         """Execute the side effects of this action.
 
         Args:
             dispatcher: the dispatcher which is used to
-                send messages back to the user. Use
-                ``dispatcher.utter_message()`` for sending messages.
-            tracker: the state tracker for the current
-                user. You can access slot values using
-                ``tracker.get_slot(slot_name)``, the most recent user message
-                is ``tracker.latest_message.text`` and any other
-                ``rasa_sdk.Tracker`` property.
-            domain: the bot's domain
+                send messages back to the user.
+            tracker: the state tracker for the current user.
+            domain: the bot's domain.
         Returns:
-            A dictionary of ``rasa_sdk.events.Event`` instances that is
-                returned through the endpoint
+            A dictionary of ``rasa_sdk.events.Event`` instances.
         """
 
         slots_to_validate: Dict[Text, Any] = tracker.form_slots_to_validate()
diff --git a/rasa_sdk/interfaces.py b/rasa_sdk/interfaces.py
index a19ddd267..5f7591008 100644
--- a/rasa_sdk/interfaces.py
+++ b/rasa_sdk/interfaces.py
@@ -245,6 +245,7 @@ def slots_to_validate(self) -> Dict[Text, Any]:
 
         slots: Dict[Text, Any] = {}
 
+        print(self.events)
         for event in reversed(self.events):
             # The `FormAction` in Rasa Open Source will append all slot candidates
             # at the end of the tracker events.
@@ -267,10 +268,7 @@ def name(self) -> Text:
         raise NotImplementedError("An action must implement a name")
 
     async def run(
-        self,
-        dispatcher,
-        tracker: Tracker,
-        domain: "DomainDict",
+        self, dispatcher, tracker: Tracker, domain: "DomainDict",
     ) -> List[Dict[Text, Any]]:
         """Execute the side effects of this action.
 
diff --git a/rasa_sdk/knowledge_base/actions.py b/rasa_sdk/knowledge_base/actions.py
index 0176cc961..c8a28e201 100644
--- a/rasa_sdk/knowledge_base/actions.py
+++ b/rasa_sdk/knowledge_base/actions.py
@@ -92,10 +92,8 @@ async def utter_objects(
             if utils.is_coroutine_action(
                 self.knowledge_base.get_representation_function_of_object
             ):
-                repr_function = (
-                    await self.knowledge_base.get_representation_function_of_object(
-                        object_type
-                    )
+                repr_function = await self.knowledge_base.get_representation_function_of_object(
+                    object_type
                 )
             else:
                 # see https://github.com/python/mypy/issues/5206
@@ -114,10 +112,7 @@ async def utter_objects(
             )
 
     async def run(
-        self,
-        dispatcher: CollectingDispatcher,
-        tracker: Tracker,
-        domain: "DomainDict",
+        self, dispatcher: CollectingDispatcher, tracker: Tracker, domain: "DomainDict",
     ) -> List[Dict[Text, Any]]:
         """
         Executes this action. If the user ask a question about an attribute,
@@ -273,10 +268,8 @@ async def _query_attribute(
         if utils.is_coroutine_action(
             self.knowledge_base.get_representation_function_of_object
         ):
-            repr_function = (
-                await self.knowledge_base.get_representation_function_of_object(
-                    object_type
-                )
+            repr_function = await self.knowledge_base.get_representation_function_of_object(
+                object_type
             )
         else:
             # see https://github.com/python/mypy/issues/5206
diff --git a/tests/test_actions.py b/tests/test_actions.py
index 3be07e750..de6d82644 100644
--- a/tests/test_actions.py
+++ b/tests/test_actions.py
@@ -12,10 +12,7 @@ def name(cls) -> Text:
         return "custom_async_action"
 
     async def run(
-        self,
-        dispatcher: CollectingDispatcher,
-        tracker: Tracker,
-        domain: DomainDict,
+        self, dispatcher: CollectingDispatcher, tracker: Tracker, domain: DomainDict,
     ) -> List[Dict[Text, Any]]:
         return [SlotSet("test", "foo"), SlotSet("test2", "boo")]
 
@@ -25,10 +22,7 @@ def name(cls) -> Text:
         return "custom_action"
 
     def run(
-        self,
-        dispatcher: CollectingDispatcher,
-        tracker: Tracker,
-        domain: DomainDict,
+        self, dispatcher: CollectingDispatcher, tracker: Tracker, domain: DomainDict,
     ) -> List[Dict[Text, Any]]:
         return [SlotSet("test", "bar")]
 
diff --git a/tests/test_forms.py b/tests/test_forms.py
index b7a7d15db..f5a0668ec 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -5,7 +5,7 @@
 from rasa_sdk import Tracker, ActionExecutionRejection
 from rasa_sdk.events import SlotSet, ActiveLoop
 from rasa_sdk.executor import CollectingDispatcher
-from rasa_sdk.forms import FormAction, REQUESTED_SLOT, LOOP_INTERRUPTED_KEY
+from rasa_sdk.forms import FormAction, FormSlotsValidatorAction, REQUESTED_SLOT, LOOP_INTERRUPTED_KEY
 
 
 def test_extract_requested_slot_default():
@@ -1493,3 +1493,60 @@ async def test_submit(form_class: Type[FormAction]):
 def test_form_deprecation():
     with pytest.warns(FutureWarning):
         FormAction()
+
+
+class TestFormSlotValidator(FormSlotsValidatorAction):
+    def name(self) -> Text:
+        return "some_form"
+
+    @staticmethod
+    def validate_slot1(tracker: Tracker, domain: Dict, slot_value: Any) -> bool:
+        return slot_value == "correct_value"
+
+    @staticmethod
+    def validate_slot2(tracker: Tracker, domain: Dict, slot_value: Any) -> bool:
+        return slot_value == "correct_value"
+
+
+async def test_form_slot_validator():
+    form = TestFormSlotValidator()
+
+    # tracker with active form
+    tracker = Tracker(
+        "default",
+        {},
+        {},
+        [SlotSet("slot1", "correct_value"), SlotSet("slot2", "incorrect_value")],
+        False,
+        None,
+        {"name": "some_form", "validate": True, "rejected": False},
+        "action_listen",
+    )
+
+    dispatcher = CollectingDispatcher()
+    events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
+    # check that the form was activated and validation was performed
+    assert events == [
+        SlotSet("slot2", None),
+        SlotSet("slot1", "correct_value"),
+    ]
+
+
+async def test_form_slot_validator_missing_method():
+    form = TestFormSlotValidator()
+
+    # tracker with active form
+    tracker = Tracker(
+        "default",
+        {},
+        {},
+        [SlotSet("slot1", "correct_value"), SlotSet("slot2", "incorrect_value"), SlotSet("slot3", "some_value")],
+        False,
+        None,
+        {"name": "some_form", "validate": True, "rejected": False},
+        "action_listen",
+    )
+
+    dispatcher = CollectingDispatcher()
+    with pytest.raises(AttributeError):
+        events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
\ No newline at end of file

From 3474274884180c2e3f2d6f1d2069d58b1a663f9d Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Fri, 2 Oct 2020 10:26:23 +0200
Subject: [PATCH 03/16] Black reformatting; minor test name change

---
 rasa_sdk/forms.py   |  4 +++-
 tests/test_forms.py | 10 +++++++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index f5bfd70e6..524aeb5f8 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -700,7 +700,9 @@ def name(self) -> Text:
 
         raise NotImplementedError("An action must implement a name")
 
-    async def run(self, dispatcher, tracker: "Tracker", domain: Dict) -> List[EventType]:
+    async def run(
+        self, dispatcher, tracker: "Tracker", domain: Dict
+    ) -> List[EventType]:
         """Execute the side effects of this action.
 
         Args:
diff --git a/tests/test_forms.py b/tests/test_forms.py
index f5a0668ec..e64a88d39 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -1532,7 +1532,7 @@ async def test_form_slot_validator():
     ]
 
 
-async def test_form_slot_validator_missing_method():
+async def test_form_slot_validator_attribute_error():
     form = TestFormSlotValidator()
 
     # tracker with active form
@@ -1540,7 +1540,11 @@ async def test_form_slot_validator_missing_method():
         "default",
         {},
         {},
-        [SlotSet("slot1", "correct_value"), SlotSet("slot2", "incorrect_value"), SlotSet("slot3", "some_value")],
+        [
+            SlotSet("slot1", "correct_value"),
+            SlotSet("slot2", "incorrect_value"),
+            SlotSet("slot3", "some_value"),
+        ],
         False,
         None,
         {"name": "some_form", "validate": True, "rejected": False},
@@ -1549,4 +1553,4 @@ async def test_form_slot_validator_missing_method():
 
     dispatcher = CollectingDispatcher()
     with pytest.raises(AttributeError):
-        events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
\ No newline at end of file
+        events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)

From ea2fc8ed4246552472cc2c9f09d9105f260d7a66 Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Fri, 2 Oct 2020 10:30:31 +0200
Subject: [PATCH 04/16] Changelog entry

---
 changelog/288.improvement.md | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 changelog/288.improvement.md

diff --git a/changelog/288.improvement.md b/changelog/288.improvement.md
new file mode 100644
index 000000000..d832bae19
--- /dev/null
+++ b/changelog/288.improvement.md
@@ -0,0 +1,2 @@
+Add the `FormSlotsValidatorAction` abstract class that can be used
+to validate slots which were extracted by a Form.
\ No newline at end of file

From b470378322b5de3b3187ed5678a4bef214bb134e Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Fri, 2 Oct 2020 10:35:48 +0200
Subject: [PATCH 05/16] Test fix

---
 tests/test_forms.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test_forms.py b/tests/test_forms.py
index e64a88d39..58fc91215 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -1553,4 +1553,4 @@ async def test_form_slot_validator_attribute_error():
 
     dispatcher = CollectingDispatcher()
     with pytest.raises(AttributeError):
-        events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
+        await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)

From 6ce562ba2e7884654f15ed6a44a102884e1fd338 Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Fri, 2 Oct 2020 11:13:49 +0200
Subject: [PATCH 06/16] Black reformatting

---
 rasa_sdk/forms.py                  |  3 ++-
 rasa_sdk/interfaces.py             |  5 ++++-
 rasa_sdk/knowledge_base/actions.py | 17 ++++++++++++-----
 tests/test_actions.py              | 10 ++++++++--
 4 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index 524aeb5f8..084f74ecc 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -672,7 +672,8 @@ def __str__(self) -> Text:
         return f"FormAction('{self.name()}')"
 
     def _get_entity_type_of_slot_to_fill(
-        self, slot_to_fill: Optional[Text],
+        self,
+        slot_to_fill: Optional[Text],
     ) -> Optional[Text]:
         if not slot_to_fill:
             return None
diff --git a/rasa_sdk/interfaces.py b/rasa_sdk/interfaces.py
index 5f7591008..aea3c829c 100644
--- a/rasa_sdk/interfaces.py
+++ b/rasa_sdk/interfaces.py
@@ -268,7 +268,10 @@ def name(self) -> Text:
         raise NotImplementedError("An action must implement a name")
 
     async def run(
-        self, dispatcher, tracker: Tracker, domain: "DomainDict",
+        self,
+        dispatcher,
+        tracker: Tracker,
+        domain: "DomainDict",
     ) -> List[Dict[Text, Any]]:
         """Execute the side effects of this action.
 
diff --git a/rasa_sdk/knowledge_base/actions.py b/rasa_sdk/knowledge_base/actions.py
index c8a28e201..0176cc961 100644
--- a/rasa_sdk/knowledge_base/actions.py
+++ b/rasa_sdk/knowledge_base/actions.py
@@ -92,8 +92,10 @@ async def utter_objects(
             if utils.is_coroutine_action(
                 self.knowledge_base.get_representation_function_of_object
             ):
-                repr_function = await self.knowledge_base.get_representation_function_of_object(
-                    object_type
+                repr_function = (
+                    await self.knowledge_base.get_representation_function_of_object(
+                        object_type
+                    )
                 )
             else:
                 # see https://github.com/python/mypy/issues/5206
@@ -112,7 +114,10 @@ async def utter_objects(
             )
 
     async def run(
-        self, dispatcher: CollectingDispatcher, tracker: Tracker, domain: "DomainDict",
+        self,
+        dispatcher: CollectingDispatcher,
+        tracker: Tracker,
+        domain: "DomainDict",
     ) -> List[Dict[Text, Any]]:
         """
         Executes this action. If the user ask a question about an attribute,
@@ -268,8 +273,10 @@ async def _query_attribute(
         if utils.is_coroutine_action(
             self.knowledge_base.get_representation_function_of_object
         ):
-            repr_function = await self.knowledge_base.get_representation_function_of_object(
-                object_type
+            repr_function = (
+                await self.knowledge_base.get_representation_function_of_object(
+                    object_type
+                )
             )
         else:
             # see https://github.com/python/mypy/issues/5206
diff --git a/tests/test_actions.py b/tests/test_actions.py
index de6d82644..3be07e750 100644
--- a/tests/test_actions.py
+++ b/tests/test_actions.py
@@ -12,7 +12,10 @@ def name(cls) -> Text:
         return "custom_async_action"
 
     async def run(
-        self, dispatcher: CollectingDispatcher, tracker: Tracker, domain: DomainDict,
+        self,
+        dispatcher: CollectingDispatcher,
+        tracker: Tracker,
+        domain: DomainDict,
     ) -> List[Dict[Text, Any]]:
         return [SlotSet("test", "foo"), SlotSet("test2", "boo")]
 
@@ -22,7 +25,10 @@ def name(cls) -> Text:
         return "custom_action"
 
     def run(
-        self, dispatcher: CollectingDispatcher, tracker: Tracker, domain: DomainDict,
+        self,
+        dispatcher: CollectingDispatcher,
+        tracker: Tracker,
+        domain: DomainDict,
     ) -> List[Dict[Text, Any]]:
         return [SlotSet("test", "bar")]
 

From 7ff7b94059d882a1d7417c0f059bf1797e2a8271 Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Fri, 2 Oct 2020 11:21:36 +0200
Subject: [PATCH 07/16] Types update

---
 rasa_sdk/forms.py   | 5 ++++-
 tests/test_forms.py | 5 +++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index 084f74ecc..ef7e02da0 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -702,7 +702,10 @@ def name(self) -> Text:
         raise NotImplementedError("An action must implement a name")
 
     async def run(
-        self, dispatcher, tracker: "Tracker", domain: Dict
+        self,
+        dispatcher: "CollectingDispatcher",
+        tracker: "Tracker",
+        domain: "DomainDict",
     ) -> List[EventType]:
         """Execute the side effects of this action.
 
diff --git a/tests/test_forms.py b/tests/test_forms.py
index 58fc91215..feb360e48 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -3,6 +3,7 @@
 from typing import Type, Text, Dict, Any, List, Optional
 
 from rasa_sdk import Tracker, ActionExecutionRejection
+from rasa_sdk.types import DomainDict
 from rasa_sdk.events import SlotSet, ActiveLoop
 from rasa_sdk.executor import CollectingDispatcher
 from rasa_sdk.forms import FormAction, FormSlotsValidatorAction, REQUESTED_SLOT, LOOP_INTERRUPTED_KEY
@@ -1500,11 +1501,11 @@ def name(self) -> Text:
         return "some_form"
 
     @staticmethod
-    def validate_slot1(tracker: Tracker, domain: Dict, slot_value: Any) -> bool:
+    def validate_slot1(tracker: Tracker, domain: "DomainDict", slot_value: Any) -> bool:
         return slot_value == "correct_value"
 
     @staticmethod
-    def validate_slot2(tracker: Tracker, domain: Dict, slot_value: Any) -> bool:
+    def validate_slot2(tracker: Tracker, domain: "DomainDict", slot_value: Any) -> bool:
         return slot_value == "correct_value"
 
 

From ed852a6e7dce15ec441a668a30e650824a4d86ca Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Fri, 2 Oct 2020 16:33:53 +0200
Subject: [PATCH 08/16] Update

---
 rasa_sdk/forms.py      | 76 ++++++++++++++++++++++++++++++++++--------
 rasa_sdk/interfaces.py |  1 -
 tests/test_forms.py    | 38 +++++++++++++--------
 3 files changed, 88 insertions(+), 27 deletions(-)

diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index ef7e02da0..782b93fd2 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -693,21 +693,42 @@ def _get_entity_type_of_slot_to_fill(
         return entity_type
 
 
-class FormSlotsValidatorAction(Action):
-    """An action that validates if every extracted slot is valid."""
+class FormValidationAction(Action):
+    """An action that validates if every extracted slot is valid.
+
+    Example of usage:
+    ```
+        class MyFormValidationAction(FormValidationAction):
+            def name(self) -> Text:
+                return "some_form"
+
+            def validate_slot1(
+                self,
+                slot_value: Any,
+                dispatcher: "CollectingDispatcher",
+                tracker: "Tracker",
+                domain: "DomainDict",
+            )
+                return slot_value == "correct_value"
+    ```
+        """
 
     def name(self) -> Text:
-        """Unique identifier of this action."""
+        """Unique identifier of this action.
+
+        Returns:
+            Name of the action.
+        """
 
         raise NotImplementedError("An action must implement a name")
 
-    async def run(
+    async def validate(
         self,
         dispatcher: "CollectingDispatcher",
         tracker: "Tracker",
         domain: "DomainDict",
     ) -> List[EventType]:
-        """Execute the side effects of this action.
+        """Validate slots by calling a validation function for each slot.
 
         Args:
             dispatcher: the dispatcher which is used to
@@ -715,20 +736,49 @@ async def run(
             tracker: the state tracker for the current user.
             domain: the bot's domain.
         Returns:
-            A dictionary of ``rasa_sdk.events.Event`` instances.
+            A dictionary of `rasa_sdk.events.Event` instances.
         """
-
         slots_to_validate: Dict[Text, Any] = tracker.form_slots_to_validate()
-        validation_events = []
+        validated_events = []
 
         for slot_name, slot_value in slots_to_validate.items():
             function_name = f"validate_{slot_name}"
-            fn = getattr(self, function_name)
-            if fn(tracker, domain, slot_value):
-                validation_events.append(SlotSet(slot_name, slot_value))
+            validate_func = getattr(self, function_name, lambda *x: False)
+
+            if utils.is_coroutine_action(validate_func):
+                validation_output = await validate_func(
+                    slot_value, dispatcher, tracker, domain
+                )
+            else:
+                validation_output = validate_func(slot_value, dispatcher, tracker, domain)
+
+            if validation_output:
+                validated_events.append(SlotSet(slot_name, slot_value))
             else:
                 # Return a `SlotSet` event with value `None` to indicate that this
                 # slot still needs to be filled.
-                validation_events.append(SlotSet(slot_name, None))
+                warnings.warn(
+                    f"Cannot validate `{slot_name}`: make sure the validation function is specified and "
+                    f"returns `True`"
+                )
+
+        return validated_events
+
+    async def run(
+        self,
+        dispatcher: "CollectingDispatcher",
+        tracker: "Tracker",
+        domain: "DomainDict",
+    ) -> List[EventType]:
+        """Execute the side effects of this action.
+
+        Args:
+            dispatcher: the dispatcher which is used to
+                send messages back to the user.
+            tracker: the state tracker for the current user.
+            domain: the bot's domain.
+        Returns:
+            A dictionary of `rasa_sdk.events.Event` instances.
+        """
 
-        return validation_events
+        return await self.validate(dispatcher, tracker, domain)
diff --git a/rasa_sdk/interfaces.py b/rasa_sdk/interfaces.py
index aea3c829c..a19ddd267 100644
--- a/rasa_sdk/interfaces.py
+++ b/rasa_sdk/interfaces.py
@@ -245,7 +245,6 @@ def slots_to_validate(self) -> Dict[Text, Any]:
 
         slots: Dict[Text, Any] = {}
 
-        print(self.events)
         for event in reversed(self.events):
             # The `FormAction` in Rasa Open Source will append all slot candidates
             # at the end of the tracker events.
diff --git a/tests/test_forms.py b/tests/test_forms.py
index feb360e48..19f01cd08 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -6,7 +6,7 @@
 from rasa_sdk.types import DomainDict
 from rasa_sdk.events import SlotSet, ActiveLoop
 from rasa_sdk.executor import CollectingDispatcher
-from rasa_sdk.forms import FormAction, FormSlotsValidatorAction, REQUESTED_SLOT, LOOP_INTERRUPTED_KEY
+from rasa_sdk.forms import FormAction, FormValidationAction, REQUESTED_SLOT, LOOP_INTERRUPTED_KEY
 
 
 def test_extract_requested_slot_default():
@@ -1496,21 +1496,31 @@ def test_form_deprecation():
         FormAction()
 
 
-class TestFormSlotValidator(FormSlotsValidatorAction):
+class TestFormValidationAction(FormValidationAction):
     def name(self) -> Text:
         return "some_form"
 
-    @staticmethod
-    def validate_slot1(tracker: Tracker, domain: "DomainDict", slot_value: Any) -> bool:
+    def validate_slot1(
+        self,
+        slot_value: Any,
+        dispatcher: "CollectingDispatcher",
+        tracker: "Tracker",
+        domain: "DomainDict",
+    ) -> bool:
         return slot_value == "correct_value"
 
-    @staticmethod
-    def validate_slot2(tracker: Tracker, domain: "DomainDict", slot_value: Any) -> bool:
+    def validate_slot2(
+        self,
+        slot_value: Any,
+        dispatcher: "CollectingDispatcher",
+        tracker: "Tracker",
+        domain: "DomainDict",
+    ) -> bool:
         return slot_value == "correct_value"
 
 
-async def test_form_slot_validator():
-    form = TestFormSlotValidator()
+async def test_form_validation_action():
+    form = TestFormValidationAction()
 
     # tracker with active form
     tracker = Tracker(
@@ -1528,13 +1538,12 @@ async def test_form_slot_validator():
     events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
     # check that the form was activated and validation was performed
     assert events == [
-        SlotSet("slot2", None),
         SlotSet("slot1", "correct_value"),
     ]
 
 
-async def test_form_slot_validator_attribute_error():
-    form = TestFormSlotValidator()
+async def test_form_validation_action_attribute_error():
+    form = TestFormValidationAction()
 
     # tracker with active form
     tracker = Tracker(
@@ -1553,5 +1562,8 @@ async def test_form_slot_validator_attribute_error():
     )
 
     dispatcher = CollectingDispatcher()
-    with pytest.raises(AttributeError):
-        await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
+    events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
+    # check that the form was activated and validation was performed
+    assert events == [
+        SlotSet("slot1", "correct_value"),
+    ]

From 69c28a42c7360a82d18d42a608af40d22aae5677 Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Fri, 2 Oct 2020 16:34:23 +0200
Subject: [PATCH 09/16] Code style update

---
 rasa_sdk/forms.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index 782b93fd2..d7e859837 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -711,7 +711,7 @@ def validate_slot1(
             )
                 return slot_value == "correct_value"
     ```
-        """
+    """
 
     def name(self) -> Text:
         """Unique identifier of this action.
@@ -750,7 +750,9 @@ async def validate(
                     slot_value, dispatcher, tracker, domain
                 )
             else:
-                validation_output = validate_func(slot_value, dispatcher, tracker, domain)
+                validation_output = validate_func(
+                    slot_value, dispatcher, tracker, domain
+                )
 
             if validation_output:
                 validated_events.append(SlotSet(slot_name, slot_value))

From c02d12fc30b54b4cae8d323406bc01cec194cfa3 Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Fri, 2 Oct 2020 16:40:37 +0200
Subject: [PATCH 10/16] Small update: type annotation

---
 rasa_sdk/forms.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index d7e859837..5f97aa3e1 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -708,7 +708,7 @@ def validate_slot1(
                 dispatcher: "CollectingDispatcher",
                 tracker: "Tracker",
                 domain: "DomainDict",
-            )
+            ) -> bool:
                 return slot_value == "correct_value"
     ```
     """

From 4f99ddae2fbab837cb69d1facb6098c3ae36aae0 Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Mon, 5 Oct 2020 10:14:24 +0200
Subject: [PATCH 11/16] Updated logic

---
 changelog/288.improvement.md | 22 +++++++++++++++++++++-
 rasa_sdk/forms.py            | 32 ++++++--------------------------
 tests/test_forms.py          | 19 +++++++++++++------
 3 files changed, 40 insertions(+), 33 deletions(-)

diff --git a/changelog/288.improvement.md b/changelog/288.improvement.md
index d832bae19..d6ebc16b5 100644
--- a/changelog/288.improvement.md
+++ b/changelog/288.improvement.md
@@ -1,2 +1,22 @@
 Add the `FormSlotsValidatorAction` abstract class that can be used
-to validate slots which were extracted by a Form.
\ No newline at end of file
+to validate slots which were extracted by a Form.
+
+Example:
+
+```python
+class MyFormValidationAction(FormValidationAction):
+    def name(self) -> Text:
+        return "some_form"
+
+    def validate_slot1(
+        self,
+        slot_value: Any,
+        dispatcher: "CollectingDispatcher",
+        tracker: "Tracker",
+        domain: "DomainDict",
+    ) -> Dict[Text, Any]:
+        if slot_value == "correct_value":
+            return {
+                "slot1": "validated_value",
+            }
+```
\ No newline at end of file
diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index 5f97aa3e1..8a4ebb937 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -694,24 +694,7 @@ def _get_entity_type_of_slot_to_fill(
 
 
 class FormValidationAction(Action):
-    """An action that validates if every extracted slot is valid.
-
-    Example of usage:
-    ```
-        class MyFormValidationAction(FormValidationAction):
-            def name(self) -> Text:
-                return "some_form"
-
-            def validate_slot1(
-                self,
-                slot_value: Any,
-                dispatcher: "CollectingDispatcher",
-                tracker: "Tracker",
-                domain: "DomainDict",
-            ) -> bool:
-                return slot_value == "correct_value"
-    ```
-    """
+    """An action that validates if every extracted slot is valid."""
 
     def name(self) -> Text:
         """Unique identifier of this action.
@@ -738,10 +721,9 @@ async def validate(
         Returns:
             A dictionary of `rasa_sdk.events.Event` instances.
         """
-        slots_to_validate: Dict[Text, Any] = tracker.form_slots_to_validate()
-        validated_events = []
+        slots: Dict[Text, Any] = tracker.form_slots_to_validate()
 
-        for slot_name, slot_value in slots_to_validate.items():
+        for slot_name, slot_value in slots.items():
             function_name = f"validate_{slot_name}"
             validate_func = getattr(self, function_name, lambda *x: False)
 
@@ -755,16 +737,14 @@ async def validate(
                 )
 
             if validation_output:
-                validated_events.append(SlotSet(slot_name, slot_value))
+                slots.update(validation_output)
             else:
-                # Return a `SlotSet` event with value `None` to indicate that this
-                # slot still needs to be filled.
                 warnings.warn(
                     f"Cannot validate `{slot_name}`: make sure the validation function is specified and "
-                    f"returns `True`"
+                    f"returns a list of `rasa_sdk.events.Event` instances."
                 )
 
-        return validated_events
+        return [SlotSet(slot, value) for slot, value in slots.items()]
 
     async def run(
         self,
diff --git a/tests/test_forms.py b/tests/test_forms.py
index 19f01cd08..dc8e1dfcf 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -1506,8 +1506,11 @@ def validate_slot1(
         dispatcher: "CollectingDispatcher",
         tracker: "Tracker",
         domain: "DomainDict",
-    ) -> bool:
-        return slot_value == "correct_value"
+    ) -> Dict[Text, Any]:
+        if slot_value == "correct_value":
+            return {
+                "slot1": "validated_value",
+            }
 
     def validate_slot2(
         self,
@@ -1515,8 +1518,11 @@ def validate_slot2(
         dispatcher: "CollectingDispatcher",
         tracker: "Tracker",
         domain: "DomainDict",
-    ) -> bool:
-        return slot_value == "correct_value"
+    ) -> Dict[Text, Any]:
+        if slot_value == "correct_value":
+            return {
+                "slot2": "validated_value",
+            }
 
 
 async def test_form_validation_action():
@@ -1538,7 +1544,8 @@ async def test_form_validation_action():
     events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
     # check that the form was activated and validation was performed
     assert events == [
-        SlotSet("slot1", "correct_value"),
+        SlotSet("slot1", "validated_value"),
+        SlotSet("slot2", "incorrect_value")
     ]
 
 
@@ -1565,5 +1572,5 @@ async def test_form_validation_action_attribute_error():
     events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
     # check that the form was activated and validation was performed
     assert events == [
-        SlotSet("slot1", "correct_value"),
+        SlotSet("slot1", "validated_value"),
     ]

From 1c74bbb7755841d9649feb9d7dd0169cccfdd838 Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Mon, 5 Oct 2020 10:28:27 +0200
Subject: [PATCH 12/16] Check warning

---
 tests/test_forms.py | 50 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 44 insertions(+), 6 deletions(-)

diff --git a/tests/test_forms.py b/tests/test_forms.py
index dc8e1dfcf..7a986bce5 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -1524,6 +1524,18 @@ def validate_slot2(
                 "slot2": "validated_value",
             }
 
+    async def validate_slot3(
+        self,
+        slot_value: Any,
+        dispatcher: "CollectingDispatcher",
+        tracker: "Tracker",
+        domain: "DomainDict",
+    ) -> Dict[Text, Any]:
+        if slot_value == "correct_value":
+            return {
+                "slot3": "validated_value",
+            }
+
 
 async def test_form_validation_action():
     form = TestFormValidationAction()
@@ -1544,8 +1556,31 @@ async def test_form_validation_action():
     events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
     # check that the form was activated and validation was performed
     assert events == [
+        SlotSet("slot2", "incorrect_value"),
         SlotSet("slot1", "validated_value"),
-        SlotSet("slot2", "incorrect_value")
+    ]
+
+
+async def test_form_validation_action_async():
+    form = TestFormValidationAction()
+
+    # tracker with active form
+    tracker = Tracker(
+        "default",
+        {},
+        {},
+        [SlotSet("slot3", "correct_value")],
+        False,
+        None,
+        {"name": "some_form", "validate": True, "rejected": False},
+        "action_listen",
+    )
+
+    dispatcher = CollectingDispatcher()
+    events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
+    # check that the form was activated and validation was performed
+    assert events == [
+        SlotSet("slot3", "validated_value")
     ]
 
 
@@ -1569,8 +1604,11 @@ async def test_form_validation_action_attribute_error():
     )
 
     dispatcher = CollectingDispatcher()
-    events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
-    # check that the form was activated and validation was performed
-    assert events == [
-        SlotSet("slot1", "validated_value"),
-    ]
+    with pytest.warns(None):
+        events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
+        # check that the form was activated and validation was performed
+        assert events == [
+            SlotSet("slot3", "some_value"),
+            SlotSet("slot2", "incorrect_value"),
+            SlotSet("slot1", "validated_value"),
+        ]

From f07893d9308b854a50ab05eecb553bd0f03cfd98 Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Mon, 5 Oct 2020 13:09:29 +0200
Subject: [PATCH 13/16] Update

---
 changelog/288.improvement.md |  3 +++
 rasa_sdk/forms.py            | 38 ++++++++++++------------------------
 tests/test_forms.py          | 26 ++++++++++++------------
 3 files changed, 29 insertions(+), 38 deletions(-)

diff --git a/changelog/288.improvement.md b/changelog/288.improvement.md
index d6ebc16b5..ef345b237 100644
--- a/changelog/288.improvement.md
+++ b/changelog/288.improvement.md
@@ -19,4 +19,7 @@ class MyFormValidationAction(FormValidationAction):
             return {
                 "slot1": "validated_value",
             }
+        return {
+            "slot1": None,
+        }
 ```
\ No newline at end of file
diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index 8a4ebb937..098e50a25 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -3,6 +3,7 @@
 import warnings
 from typing import Dict, Text, Any, List, Union, Optional, Tuple, cast
 
+from abc import ABC
 from rasa_sdk import utils
 from rasa_sdk.events import SlotSet, EventType, ActiveLoop
 from rasa_sdk.interfaces import Action, ActionExecutionRejection
@@ -693,18 +694,9 @@ def _get_entity_type_of_slot_to_fill(
         return entity_type
 
 
-class FormValidationAction(Action):
+class FormValidationAction(Action, ABC):
     """An action that validates if every extracted slot is valid."""
 
-    def name(self) -> Text:
-        """Unique identifier of this action.
-
-        Returns:
-            Name of the action.
-        """
-
-        raise NotImplementedError("An action must implement a name")
-
     async def validate(
         self,
         dispatcher: "CollectingDispatcher",
@@ -716,16 +708,22 @@ async def validate(
         Args:
             dispatcher: the dispatcher which is used to
                 send messages back to the user.
-            tracker: the state tracker for the current user.
+            tracker: the conversation tracker for the current user.
             domain: the bot's domain.
         Returns:
-            A dictionary of `rasa_sdk.events.Event` instances.
+            `SlotSet` events for every validated slot.
         """
         slots: Dict[Text, Any] = tracker.form_slots_to_validate()
 
         for slot_name, slot_value in slots.items():
             function_name = f"validate_{slot_name}"
-            validate_func = getattr(self, function_name, lambda *x: False)
+            validate_func = getattr(self, function_name, None)
+
+            if not validate_func:
+                warnings.warn(
+                    f"Cannot validate `{slot_name}`: there is no validation function specified."
+                )
+                continue
 
             if utils.is_coroutine_action(validate_func):
                 validation_output = await validate_func(
@@ -740,8 +738,7 @@ async def validate(
                 slots.update(validation_output)
             else:
                 warnings.warn(
-                    f"Cannot validate `{slot_name}`: make sure the validation function is specified and "
-                    f"returns a list of `rasa_sdk.events.Event` instances."
+                    f"Cannot validate `{slot_name}`: make sure the validation function returns the correct output."
                 )
 
         return [SlotSet(slot, value) for slot, value in slots.items()]
@@ -752,15 +749,4 @@ async def run(
         tracker: "Tracker",
         domain: "DomainDict",
     ) -> List[EventType]:
-        """Execute the side effects of this action.
-
-        Args:
-            dispatcher: the dispatcher which is used to
-                send messages back to the user.
-            tracker: the state tracker for the current user.
-            domain: the bot's domain.
-        Returns:
-            A dictionary of `rasa_sdk.events.Event` instances.
-        """
-
         return await self.validate(dispatcher, tracker, domain)
diff --git a/tests/test_forms.py b/tests/test_forms.py
index 7a986bce5..f66e5c43f 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -1511,6 +1511,9 @@ def validate_slot1(
             return {
                 "slot1": "validated_value",
             }
+        return {
+            "slot1": None,
+        }
 
     def validate_slot2(
         self,
@@ -1523,6 +1526,9 @@ def validate_slot2(
             return {
                 "slot2": "validated_value",
             }
+        return {
+            "slot2": None,
+        }
 
     async def validate_slot3(
         self,
@@ -1535,6 +1541,7 @@ async def validate_slot3(
             return {
                 "slot3": "validated_value",
             }
+        # this function doesn't return anything when the slot value is incorrect
 
 
 async def test_form_validation_action():
@@ -1548,15 +1555,14 @@ async def test_form_validation_action():
         [SlotSet("slot1", "correct_value"), SlotSet("slot2", "incorrect_value")],
         False,
         None,
-        {"name": "some_form", "validate": True, "rejected": False},
+        {"name": "some_form", "is_interrupted": False, "rejected": False},
         "action_listen",
     )
 
     dispatcher = CollectingDispatcher()
     events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
-    # check that the form was activated and validation was performed
     assert events == [
-        SlotSet("slot2", "incorrect_value"),
+        SlotSet("slot2", None),
         SlotSet("slot1", "validated_value"),
     ]
 
@@ -1572,16 +1578,13 @@ async def test_form_validation_action_async():
         [SlotSet("slot3", "correct_value")],
         False,
         None,
-        {"name": "some_form", "validate": True, "rejected": False},
+        {"name": "some_form", "is_interrupted": False, "rejected": False},
         "action_listen",
     )
 
     dispatcher = CollectingDispatcher()
     events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
-    # check that the form was activated and validation was performed
-    assert events == [
-        SlotSet("slot3", "validated_value")
-    ]
+    assert events == [SlotSet("slot3", "validated_value")]
 
 
 async def test_form_validation_action_attribute_error():
@@ -1599,16 +1602,15 @@ async def test_form_validation_action_attribute_error():
         ],
         False,
         None,
-        {"name": "some_form", "validate": True, "rejected": False},
+        {"name": "some_form", "is_interrupted": False, "rejected": False},
         "action_listen",
     )
 
     dispatcher = CollectingDispatcher()
-    with pytest.warns(None):
+    with pytest.warns(UserWarning):
         events = await form.run(dispatcher=dispatcher, tracker=tracker, domain=None)
-        # check that the form was activated and validation was performed
         assert events == [
             SlotSet("slot3", "some_value"),
-            SlotSet("slot2", "incorrect_value"),
+            SlotSet("slot2", None),
             SlotSet("slot1", "validated_value"),
         ]

From 620dec22ee8be8066a28816048a9c6cb75571c96 Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Mon, 5 Oct 2020 14:02:15 +0200
Subject: [PATCH 14/16] Naming update

---
 tests/test_forms.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test_forms.py b/tests/test_forms.py
index f66e5c43f..af2ea248a 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -1587,7 +1587,7 @@ async def test_form_validation_action_async():
     assert events == [SlotSet("slot3", "validated_value")]
 
 
-async def test_form_validation_action_attribute_error():
+async def test_form_validation_without_validate_function():
     form = TestFormValidationAction()
 
     # tracker with active form

From 02e30bde1c767ec06c868372dfc5165f857bb4f5 Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Mon, 5 Oct 2020 14:05:11 +0200
Subject: [PATCH 15/16] Post-rebase update

---
 rasa_sdk/forms.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rasa_sdk/forms.py b/rasa_sdk/forms.py
index 098e50a25..82df25534 100644
--- a/rasa_sdk/forms.py
+++ b/rasa_sdk/forms.py
@@ -713,7 +713,7 @@ async def validate(
         Returns:
             `SlotSet` events for every validated slot.
         """
-        slots: Dict[Text, Any] = tracker.form_slots_to_validate()
+        slots: Dict[Text, Any] = tracker.slots_to_validate()
 
         for slot_name, slot_value in slots.items():
             function_name = f"validate_{slot_name}"

From 9dc99c7a652ea0f937ab9efb1766c57a8d975e85 Mon Sep 17 00:00:00 2001
From: alwx <alwxndr@gmail.com>
Date: Mon, 5 Oct 2020 14:17:22 +0200
Subject: [PATCH 16/16] Code quality update

---
 tests/test_forms.py | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tests/test_forms.py b/tests/test_forms.py
index af2ea248a..6fdf01c11 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -6,7 +6,12 @@
 from rasa_sdk.types import DomainDict
 from rasa_sdk.events import SlotSet, ActiveLoop
 from rasa_sdk.executor import CollectingDispatcher
-from rasa_sdk.forms import FormAction, FormValidationAction, REQUESTED_SLOT, LOOP_INTERRUPTED_KEY
+from rasa_sdk.forms import (
+    FormAction,
+    FormValidationAction,
+    REQUESTED_SLOT,
+    LOOP_INTERRUPTED_KEY,
+)
 
 
 def test_extract_requested_slot_default():