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diff --git a/t/spy-double-colon.sh b/t/spy-double-colon.sh
new file mode 100644
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+#! /bin/sh
+# Copyright (C) 2003-2013 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Check whether double colon rules work.  The Unix V7 make manual
+# mentions double-colon rules, but POSIX does not.  They seem to be
+# supported by all Make implementation as far as we can tell. This test
+# case is a spy: we want to detect if there exist implementations where
+# these do not work.  We might use these rules to simplify the rebuild
+# rules (instead of the $? hack).
+
+# Tom Tromey write:
+# | In the distant past we used :: rules extensively.
+# | Fran?ois convinced me to get rid of them:
+# |
+# | Thu Nov 23 18:02:38 1995  Tom Tromey  <tromey@cambric>
+# | [ ... ]
+# |         * subdirs.am: Removed "::" rules
+# |         * header.am, libraries.am, mans.am, texinfos.am, footer.am:
+# |         Removed "::" rules
+# |         * scripts.am, programs.am, libprograms.am: Removed "::" rules
+# |
+# |
+# | I no longer remember the rationale for this.  It may have only been a
+# | belief that they were unportable.
+
+# On a related topic, the Autoconf manual has the following text:
+# |     'VPATH' and double-colon rules
+# |           Any assignment to 'VPATH' causes Sun 'make' to only execute
+# |           the first set of double-colon rules.  (This comment has been
+# |           here since 1994 and the context has been lost.  It's probably
+# |           about SunOS 4.  If you can reproduce this, please send us a
+# |           test case for illustration.)
+
+# We already know that overlapping ::-rule like
+#
+#   a :: b
+#   	echo rule1 >> $@
+#   a :: c
+#   	echo rule2 >> $@
+#   a :: b c
+#   	echo rule3 >> $@
+#
+# do not work equally on all platforms.  It seems that in all cases
+# Make attempts to run all matching rules.  However at least GNU Make,
+# NetBSD Make, and FreeBSD Make will detect that $@ was updated by the
+# first matching rule and skip remaining matches (with the above
+# example that means that unless 'a' was declared PHONY, only "rule1"
+# will be appended to 'a' if both b and c have changed).  Other
+# implementations like OSF1 Make and HP-UX Make do not perform such a
+# check and execute all matching rules whatever they do ("rule1",
+# "rule2", abd "rule3" will all be appended to 'a' if b and c have
+# changed).
+
+# So it seems only non-overlapping ::-rule may be portable.  This is
+# what we check now.
+
+. test-init.sh
+
+cat >Makefile <<\EOF
+a :: b
+	echo rule1 >> $@
+a :: c
+	echo rule2 >> $@
+EOF
+
+touch b c
+$sleep
+: > a
+$MAKE
+test x"$(cat a)" = x
+$sleep
+touch b
+$MAKE
+test "$(cat a)" = "rule1"
+# Ensure a is strictly newer than b, so HP-UX make does not execute rule2.
+$sleep
+: > a
+$sleep
+touch c
+$MAKE
+test "$(cat a)" = "rule2"
+
+# Unfortunately, the following is not portable to FreeBSD/NetBSD/OpenBSD
+# make, see explanation above.
+
+#: > a
+#$sleep
+#touch b c
+#$MAKE
+#grep rule1 a
+#grep rule2 a
+
+: