test the SPOT_BDD_TRACE envvar

* tests/core/bdd.test: New file.
* tests/Makefile.am: Add it.

tests/Makefile.am

@@ -196,6 +196,7 @@ TESTS_kripke = \
   core/kripke.test
 
 TESTS_misc = \
+  core/bdd.test \
   core/bitvect.test \
   core/intvcomp.test \
   core/minusx.test \

tests/core/bdd.test

@@ -0,0 +1,29 @@
+#!/bin/sh
+# -*- coding: utf-8 -*-
+# 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/>.
+
+. ./defs
+set -e
+
+# Make sure that setting the SPOT_BDD_TRACE envvar actually does
+# something.
+SPOT_BDD_TRACE=1 ltl2tgba a >out 2>err
+grep spot: out && exit 1
+grep 'spot: BDD package initialized' err
+grep 'spot: BDD stats:' err