Implemented a first and basic version of a Rete rule engine

tests/sheerkapickle/test_SheerkaPickler.py

@@ -31,6 +31,14 @@ class Obj:
 
 
 class TestSheerkaPickler(TestUsingMemoryBasedSheerka):
+    user_input_id = 0
+    return_value_id = 0
+
+    @classmethod
+    def setup(cls):
+        sheerka = cls().get_sheerka()
+        cls.user_input_id = sheerka.get_by_key("__USER_INPUT").id
+        cls.return_value_id = sheerka.get_by_key("__RETURN_VALUE").id
 
     @pytest.mark.parametrize("obj, expected", [
         (1, 1),
@@ -194,13 +202,13 @@ class TestSheerkaPickler(TestUsingMemoryBasedSheerka):
         sheerka, context = self.init_test().unpack()
 
         sheerka.push_ontology(context, "new ontology")
-        ontology = sheerka.pop_ontology().body.body
+        ontology = sheerka.pop_ontology(context).body.body
         obj = sheerka.ret(sheerka.name, True, ontology)
 
         flatten = SheerkaPickler(sheerka).flatten(obj)
         assert flatten == {
             '_sheerka/obj': 'core.builtin_concepts.ReturnValueConcept',
-            'concept/id': ('__RETURN_VALUE', '43'),
+            'concept/id': ('__RETURN_VALUE', self.return_value_id),
             'status': True,
             'value': 'new ontology',
             'who': '__SHEERKA'}