Tests: add ID-property TestRNAData.test_custom_properties_access

Ensures RNA/ID-property key lookups are compatible.

tests/python/bl_pyapi_idprop.py

@@ -266,6 +266,27 @@ if np is not None:
 
 class TestRNAData(TestHelper, unittest.TestCase):
 
+    def test_custom_properties_access(self):
+        # Ensure the RNA path resolving behaves as expected & is compatible with ID-property keys.
+        keys_to_test = (
+            "test",
+            "\\"
+            '"',
+            '""',
+            '"""',
+            '[',
+            ']',
+            '[]',
+            '["]',
+            '[""]',
+            '["""]',
+            '[""""]',
+        )
+        for key_id in keys_to_test:
+            self.id[key_id] = 1
+            self.assertEqual(self.id[key_id], self.id.path_resolve('["%s"]' % bpy.utils.escape_identifier(key_id)))
+            del self.id[key_id]
+
     def test_custom_properties_none(self):
         bpy.data.objects.new("test", None)
         test_object = bpy.data.objects["test"]