tests: work around to compiler warnings

* tests/core/cube.cc, tests/core/twagraph.cc: Fix warning about
unused variable in absence of assert().

tests/core/cube.cc

@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2015, 2016, 2018, 2020 Laboratoire de Recherche et
+// Copyright (C) 2015-2016, 2018, 2020-2021 Laboratoire de Recherche et
 // Développement de l'Epita.
 //
 // This file is part of Spot, a model checking library.
@@ -100,7 +100,7 @@ static void test_bdd_to_cube()
 
   // The BDD to convert
   bdd x;
-  bool result;
+  int result;
 
   // Test bddtrue
   x = bddtrue;
@@ -123,6 +123,8 @@ static void test_bdd_to_cube()
   result = test_translation(x, cubeset, binder, reverse_binder, aps);
   assert(result);
 
+  (void)result;
+
   // Free all variables
   d->unregister_variable(idx_e, d);
   d->unregister_variable(idx_d, d);

tests/core/twagraph.cc

@@ -212,6 +212,7 @@ static void f6()
 
   unsigned out = tg->merge_states_of();
   assert(out == 3);
+  (void) out;
 }
 
 // Compare merge_states() and merge_states_of()