diff --git a/tests/bonsai/str.mk b/tests/bonsai/str.mk
index fac642e..38ad9ca 100755
--- a/tests/bonsai/str.mk
+++ b/tests/bonsai/str.mk
@@ -8,8 +8,13 @@
 .PRAGMA: command_comment
 
 .PHONY: str_tests
-str_tests: str_help
+str_tests: str_help str_isalpha
 
 .PHONY: str_help
 str_help: $(BIN)/str
 	! $(BIN)/str -h
+
+.PHONY: str_isalpha
+str_isalpha: $(BIN)/str
+	$(BIN)/str   isalpha c
+	! $(BIN)/str isalpha 3