Refactor + tests (#6)

- Minor codebase clean-up
- Slight reorganisation of examples + tests so that we don't break stuff by accident
- CI tests

reactics-smt/rs/reaction_system_with_concentrations_param.py

@@ -34,9 +34,9 @@ class ReactionSystemWithConcentrationsParam(ReactionSystem):
     def add_bg_set_entity(self, e):
         name = ""
         def_max_conc = -1
-        if type(e) is tuple and len(e) == 2:
+        if isinstance(e, tuple) and len(e) == 2:
             name, def_max_conc = e
-        elif type(e) is str:
+        elif isinstance(e, str):
             name = e
             print("\nWARNING: no maximal concentration level specified for:", e, "\n")
         else:
@@ -80,18 +80,10 @@ class ReactionSystemWithConcentrationsParam(ReactionSystem):
     def is_valid_entity_with_concentration(self, e):
         """Sanity check for entities with concentration"""
 
-        if type(e) is tuple:
-            if len(e) == 2 and type(e[1]) is int:
-                return True
+        if isinstance(e, (tuple, list)) and len(e) == 2 and isinstance(e[1], int):
+            return True
 
-        if type(e) is list:
-            if len(e) == 2 and type(e[1]) is int:
-                return True
-
-        print("FATAL. Invalid entity+concentration: {:s}".format(e))
-        exit(1)
-
-        return False
+        raise RuntimeError("Invalid entity+concentration: " + repr(e))
 
     def is_valid_concentration_for_entity(self, entity, level):
         """Checks the concentration level for entity"""