tests: Introduce running tests with GNU autotest in OpenBSC

The quality of the tests is of different value but it is good to
get started and improve from here.
diff --git a/openbsc/tests/Makefile.am b/openbsc/tests/Makefile.am
index 1968119..64667c9 100644
--- a/openbsc/tests/Makefile.am
+++ b/openbsc/tests/Makefile.am
@@ -2,4 +2,48 @@
 
 if BUILD_NAT
 SUBDIRS += bsc-nat
+ENABLE_NAT_TEST = echo 'm4_define([ENABLE_NAT_TEST], [1])';
+else
+ENABLE_NAT_TEST = echo '';
 endif
+
+
+# The `:;' works around a Bash 3.2 bug when the output is not writeable.
+$(srcdir)/package.m4: $(top_srcdir)/configure.ac $(top_builddir)/config.log
+	:;{ \
+               echo '# Signature of the current package.' && \
+               echo 'm4_define([AT_PACKAGE_NAME],' && \
+               echo '  [$(PACKAGE_NAME)])' && \
+               echo 'm4_define([AT_PACKAGE_TARNAME],' && \
+               echo '  [$(PACKAGE_TARNAME)])' && \
+               echo 'm4_define([AT_PACKAGE_VERSION],' && \
+               echo '  [$(PACKAGE_VERSION)])' && \
+               echo 'm4_define([AT_PACKAGE_STRING],' && \
+               echo '  [$(PACKAGE_STRING)])' && \
+               echo 'm4_define([AT_PACKAGE_BUGREPORT],' && \
+               echo '  [$(PACKAGE_BUGREPORT)])'; \
+               echo 'm4_define([AT_PACKAGE_URL],' && \
+               echo '  [$(PACKAGE_URL)])'; \
+               $(ENABLE_NAT_TEST) \
+             } >'$(srcdir)/package.m4'
+
+EXTRA_DIST = testsuite.at $(srcdir)/package.m4 $(TESTSUITE)
+TESTSUITE = $(srcdir)/testsuite
+
+check-local: atconfig $(TESTSUITE)
+	$(SHELL) '$(TESTSUITE)' $(TESTSUITEFLAGS)
+
+installcheck-local: atconfig $(TESTSUITE)
+	$(SHELL) '$(TESTSUITE)' AUTOTEST_PATH='$(bindir)' \
+		$(TESTSUITEFLAGS)
+
+clean-local:
+	test ! -f '$(TESTSUITE)' || \
+		$(SHELL) '$(TESTSUITE)' --clean
+	$(RM) -f atconfig
+
+AUTOM4TE = $(SHELL) $(top_srcdir)/missing --run autom4te
+AUTOTEST = $(AUTOM4TE) --language=autotest
+$(TESTSUITE): $(srcdir)/testsuite.at $(srcdir)/package.m4
+	$(AUTOTEST) -I '$(srcdir)' -o $@.tmp $@.at
+	mv $@.tmp $@