feat: add CourseModeCheckoutStarted filter

openedx_filters/learning/filters.py

@@ -1445,3 +1445,40 @@ def run_filter(cls, schedules: QuerySet) -> QuerySet | None:
         """
         data = super().run_pipeline(schedules=schedules)
         return data.get("schedules")
+
+
+class CourseModeCheckoutStarted(OpenEdxPublicFilter):
+    """
+    Filter used to enrich the course mode checkout context before the checkout flow begins.
+
+    Purpose:
+        This filter is triggered when a user selects a course mode and the checkout process
+        starts. Pipeline steps can modify the context dict to inject additional data required
+        by external systems (e.g. pricing APIs) to customise the checkout experience.
+
+    Filter Type:
+        org.openedx.learning.course_mode.checkout.started.v1
+
+    Trigger:
+        - Repository: openedx/edx-platform
+        - Path: common/djangoapps/course_modes/views.py
+        - Function or Method: ChooseModeView.post
+    """
+
+    filter_type = "org.openedx.learning.course_mode.checkout.started.v1"
+
+    @classmethod
+    def run_filter(cls, context: dict, request: Any, course_mode: Any) -> dict:
+        """
+        Process the checkout context through the configured pipeline steps.
+
+        Arguments:
+            context (dict): the checkout context dict.
+            request (HttpRequest): the current HTTP request.
+            course_mode (CourseMode): the selected course mode object.
+
+        Returns:
+            dict: the (possibly enriched) checkout context.
+        """
+        data = super().run_pipeline(context=context, request=request, course_mode=course_mode)
+        return data.get("context")

openedx_filters/learning/tests/test_filters.py

@@ -19,6 +19,7 @@
     CourseEnrollmentQuerysetRequested,
     CourseEnrollmentStarted,
     CourseHomeUrlCreationStarted,
+    CourseModeCheckoutStarted,
     CourseRunAPIRenderStarted,
     CourseUnenrollmentStarted,
     DashboardRenderStarted,
@@ -801,3 +802,29 @@ def test_schedule_requested(self):
         result = ScheduleQuerySetRequested.run_filter(schedules)
 
         self.assertEqual(schedules, result)
+
+
+@ddt
+class TestCourseModeFilters(TestCase):
+    """
+    Test class to verify standard behavior of the course mode filters.
+
+    You'll find test suites for:
+    - `CourseModeCheckoutStarted`
+    """
+
+    def test_course_mode_checkout_started(self):
+        """
+        Test CourseModeCheckoutStarted filter behavior under normal conditions.
+
+        Expected behavior:
+            - The filter must have the signature specified.
+            - The filter should return the (possibly enriched) context dict.
+        """
+        context = {"course_id": "course-v1:edX+DemoX+Demo_Course"}
+        request = Mock()
+        course_mode = Mock()
+
+        result = CourseModeCheckoutStarted.run_filter(context, request, course_mode)
+
+        self.assertEqual(context, result)