Use old Vim for tests, perform sanity test with empty &encoding

tests/run_vim_tests.sh

@@ -1,13 +1,42 @@
 #!/bin/sh
 . tests/bot-ci/scripts/common/main.sh
-VIM=$PWD/tests/bot-ci/deps/vim/tip-$PYTHON_VERSION/vim
 FAILED=0
-for script in tests/test_*.vim ; do
-	if ! $VIM -u NONE -S $script || test -f message.fail ; then
+
+if test -z "$VIM" ; then
+	NEW_VIM="$PWD/tests/bot-ci/deps/vim/tip-$PYTHON_VERSION/vim"
+	OLD_VIM="$PWD/tests/bot-ci/deps/vim/v7-0-112-$PYTHON_VERSION/vim"
+	if test -e "$OLD_VIM" ; then
+		VIMS="NEW_VIM OLD_VIM"
+	else
+		VIMS="NEW_VIM"
+	fi
+else
+	NEW_VIM="$VIM"
+	OLD_VIM="$VIM"
+fi
+
+test_script() {
+	local vim="$1"
+	local script="$2"
+	echo "Running script $script with $vim"
+	if ! "$vim" -u NONE -S $script || test -f message.fail ; then
 		echo "Failed script $script run with $VIM" >&2
 		cat message.fail >&2
 		rm message.fail
 		FAILED=1
 	fi
+}
+
+for script in tests/test_*.vim ; do
+	if test "${script%.old.vim}" = "${script}" ; then
+		test_script "$NEW_VIM" "$script"
+	fi
 done
+
+if test -e "$OLD_VIM" ; then
+	for script in tests/test_*.old.vim ; do
+		test_script "$OLD_VIM" "$script"
+	done
+fi
+
 exit $FAILED

tests/test_empty_encoding.old.vim

@@ -0,0 +1,32 @@
+#!/usr/bin/vim -S
+if has('multibyte')
+	if empty(&encoding)
+		call writefile(['&encoding option value is empty, even though Vim has +multibyte'], 'message.fail')
+		cquit
+	endif
+	qall
+endif
+if !empty(&encoding)
+	call writefile(['&encoding option value is not empty, even though Vim does not have +multibyte'], 'message.fail')
+	cquit
+endif
+
+let g:powerline_config_paths = [expand('<sfile>:p:h:h') . '/powerline/config_files']
+
+try
+	source powerline/bindings/vim/plugin/powerline.vim
+catch
+	call writefile(['Unexpected exception:', v:exception], 'message.fail')
+	cquit
+endtry
+set ls=2
+redrawstatus!
+redir => g:messages
+	messages
+redir END
+let mess=split(g:messages, "\n")
+if len(mess)>1
+	call writefile(['Unexpected message(s):']+mess, 'message.fail')
+	cquit
+endif
+qall!