Anim: Add unit tests for keying custom properties

This PR adds unit tests for the "Custom Properties" option in the User Preferences.
It checks that the correct properties are keyed but not others.

Pull Request: https://projects.blender.org/blender/blender/pulls/120422

tests/python/bl_animation_keyframing.py

@@ -141,6 +141,43 @@ class InsertKeyTest(AbstractKeyframingTest, unittest.TestCase):
         _insert_from_user_preference_test({"SCALE"}, ["scale"])
         _insert_from_user_preference_test({"LOCATION", "ROTATION", "SCALE"}, ["location", "rotation_euler", "scale"])
 
+    def test_insert_custom_properties(self):
+        # Used to create a datablock reference property.
+        ref_object = bpy.data.objects.new("ref_object", None)
+        bpy.context.scene.collection.objects.link(ref_object)
+
+        bpy.context.preferences.edit.key_insert_channels = {"CUSTOM_PROPS"}
+        keyed_object = _create_animation_object()
+
+        keyed_properties = {
+            "int": 1,
+            "float": 1.0,
+            "bool": True,
+            "int_array": [1, 2, 3],
+            "float_array": [1.0, 2.0, 3.0],
+            "bool_array": [True, False, True],
+            "'escaped'": 1,
+            '"escaped"': 1
+        }
+
+        unkeyed_properties = {
+            "str": "unkeyed",
+            "reference": ref_object,
+        }
+
+        for path, value in keyed_properties.items():
+            keyed_object[path] = value
+
+        for path, value in unkeyed_properties.items():
+            keyed_object[path] = value
+
+        with bpy.context.temp_override(**_get_view3d_context()):
+            bpy.ops.anim.keyframe_insert()
+
+        keyed_rna_paths = [f"[\"{bpy.utils.escape_identifier(path)}\"]" for path in keyed_properties.keys()]
+        _fcurve_paths_match(keyed_object.animation_data.action.fcurves, keyed_rna_paths)
+        bpy.data.objects.remove(keyed_object, do_unlink=True)
+
 
 class VisualKeyingTest(AbstractKeyframingTest, unittest.TestCase):
     """ Check if visual keying produces the correct keyframe values. """