tests: add a test for bdd_dict::assert_emptiness()

This improves the coverage for bdd_dict::assert_emptiness() and
bdd_dict::dump().

* tests/core/bdddict.cc, tests/core/bdddict.test: New files.
* tests/Makefile.am, tests/core/.gitignore: Adjust.

tests/core/bdddict.cc

@@ -0,0 +1,31 @@
+// -*- coding: utf-8 -*-x
+// Copyright (C) 2017 Laboratoire de Recherche et
+// Développement de l'Epita (LRDE).
+//
+// This file is part of Spot, a model checking library.
+//
+// Spot is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 3 of the License, or
+// (at your option) any later version.
+//
+// Spot is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+// License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#include <iostream>
+#include <spot/tl/parse.hh>
+#include <spot/twaalgos/translate.hh>
+
+int main()
+{
+  spot::formula f = spot::parse_formula("& & G p0 p1 p2");
+  spot::translator trans;
+  spot::twa_graph_ptr aut = trans.run(f);
+  aut->get_dict()->assert_emptiness(); // Should fail.
+  return 0;
+}