Resurrect restore test and updates

tests/helpers/resurrect_helpers.sh

@@ -6,7 +6,13 @@ install_tmux_resurrect_helper() {
 }
 
 # we want "fixed" dimensions no matter the size of real display
-set_screen_dimensions() {
+set_screen_dimensions_helper() {
 	stty cols 200
 	stty rows 50
 }
+
+last_save_file_differs_helper() {
+	local original_file="$1"
+	diff "$original_file" "${HOME}/.tmux/resurrect/last"
+	[ $? -ne 0 ]
+}