make(1): add test for the command line option -t

usr.bin/make/unit-tests/opt-touch.exp

@@ -1 +1,3 @@
+`opt-touch-join' is up to date.
+`opt-touch-use' is up to date.
 exit status 0

usr.bin/make/unit-tests/opt-touch.mk

@@ -1,8 +1,18 @@
-# $NetBSD: opt-touch.mk,v 1.2 2020/08/16 14:25:16 rillig Exp $
+# $NetBSD: opt-touch.mk,v 1.3 2020/11/14 13:59:58 rillig Exp $
 #
 # Tests for the -t command line option.
 
-# TODO: Implementation
+.MAKEFLAGS: -t opt-touch-phony opt-touch-join opt-touch-use
 
-all:
-	@:;
+opt-touch-phony: .PHONY
+	: Making $@.
+
+opt-touch-join: .JOIN
+	: Making $@.
+
+opt-touch-use: .USE
+	: Making use of $@.
+
+.END:
+	@files=$$(ls opt-touch-* 2>/dev/null | grep -v -e '\.' -e '\*'); \
+	[ -z "$$files" ] || { echo "created files: $$files" 1>&2; exit 1; }