ci/testlib: add test root dir support

Allows creating (and cleaning up) a new root dir for tests, for tests
that deal with files on disk

Part-of: https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/6892

.ci/lib/testlib.sh

@@ -23,6 +23,8 @@ _test_passedn=0
 _test_failedn=0
 _test_current_test=""
 _test_statefile="$(mktemp)"
+_test_original_pwd=""
+_test_temp_root=""
 # Set by each test
 results_dir="${results_dir:-}"
 
@@ -42,6 +44,23 @@ test_debug() {
 	echo -e "${YELLOW}$*${RESET}" >&2
 }
 
+create_test_root() {
+	_test_original_pwd="$(pwd)"
+	_test_temp_root="$(mktemp -d)"
+	cd "$_test_temp_root"
+}
+
+cleanup_test_root() {
+	if [ -n "$_test_original_pwd" ]; then
+		cd "$_test_original_pwd"
+	fi
+	if [ -n "$_test_temp_root" ] && [ -d "$_test_temp_root" ]; then
+		rm -rf "$_test_temp_root"
+	fi
+	_test_original_pwd=""
+	_test_temp_root=""
+}
+
 assert_strequal() {
 	# $1: first string
 	# $2: second string