tests: add tests for warnings in build output

- add tests for build warnings and error messages
- simplify some code in build environment with plural() function

var/spack/repos/builtin.mock/packages/build-warnings/package.py

@@ -0,0 +1,47 @@
+##############################################################################
+# Copyright (c) 2013-2018, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Created by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://github.com/spack/spack
+# Please also see the NOTICE and LICENSE files for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License (as
+# published by the Free Software Foundation) version 2.1, February 1999.
+#
+# This program 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 terms and
+# conditions of the GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+from spack import *
+
+
+class BuildWarnings(Package):
+    """This package's install fails but only emits warnings."""
+
+    homepage = "http://www.example.com/trivial_install"
+    url      = "http://www.unit-test-should-replace-this-url/trivial_install-1.0.tar.gz"
+
+    version('1.0', 'foobarbaz')
+
+    def install(self, spec, prefix):
+        with open('configure', 'w') as f:
+            f.write("""#!/bin/sh\n
+echo 'checking for gcc... /Users/gamblin2/src/spack/lib/spack/env/clang/clang'
+echo 'checking whether the C compiler works... yes'
+echo 'checking for C compiler default output file name... a.out'
+echo 'WARNING: ALL CAPITAL WARNING!'
+echo 'checking for suffix of executables...'
+echo 'foo.c:89: warning: some weird warning!'
+exit 1
+""")
+        configure()