tests: bonsai/swab.mk: add example from tha man page

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

tests/bonsai/swab.mk

@@ -0,0 +1,22 @@
+# Copyright (c) 2024 DTB <trinity@trinity.moe>
+# SPDX-License-Identifier: FSFAP
+#
+# Copying and distribution of this file, with or without modification, are
+# permitted in any medium without royalty provided the copyright notice and this
+# notice are preserved.  This file is offered as-is, without any warranty.
+
+.PRAGMA: command_comment
+
+.PHONY: swab_tests
+swab_tests: swab_help swab_examples
+
+.PHONY: swab_help
+swab_help: $(BIN)/swab
+	! $(BIN)/swab -h
+
+.PHONY: swab_examples
+# These are the examples present in the man page.
+swab_examples: $(BIN)/swab
+	printf 'hello world!\n' \
+		| $(BIN)/swab \
+		| xargs -I out test 'ehll oowlr!d' = out