more unit tests for string module (rescript-lang#1052)

Author: bobzhang

jscomp/all.depend

@@ -627,7 +627,7 @@ bsb/bsb_build_util.cmx : ext/ext_list.cmx ext/ext_json.cmx \
     bsb/bsb_build_util.cmi
 bsb/bsb_config.cmx : common/js_config.cmx ext/ext_filename.cmx \
     bsb/bsb_config.cmi
-bsb/bsb_default.cmx : ext/string_set.cmx ext/literals.cmx \
+bsb/bsb_default.cmx : ext/string_set.cmx ext/literals.cmx ext/ext_string.cmx \
     ext/ext_filename.cmx bsb/bsb_build_util.cmx common/bs_pkg.cmx \
     bsb/bsb_default.cmi
 bsb/bsb_dep_infos.cmx : bsb/bsb_dep_infos.cmi