tests: allow double-colon spy.test to work with HP-UX make.

[Ralf Wildenhues]

Now that we know that what bothers HP-UX make is same-timestamp
prereqs, we can fix the age-old spurious spy.test failures for
good, and even add a test for a target out of date wrt. several
rules.  Yay!  This means that, at least in theory, we could use
double-colon rules for something eventually, if the need arises.

I'll wait a day or so before pushing to maint.

Cheers,
Ralf

    tests: allow double-colon spy.test to work with HP-UX make.
    
    * tests/spy.test: Fix comment typos.  Ensure prerequisites we
    do not want to depend on are strictly older than the target.
    Also test with a target out of date wrt. more than one rule.

diff --git a/tests/spy.test b/tests/spy.test
index 79673d5..f4bd6ef 100755
--- a/tests/spy.test
+++ b/tests/spy.test
@@ -16,8 +16,8 @@
 
 # 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 we can tell. This test case
-# is a spy: we want to detect if there exist implementations where
+# 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).
 
@@ -85,8 +85,18 @@ $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
 $MAKE
 test "`cat a`" = rule2
+: > a
+$sleep
+touch b c
+$MAKE
+grep rule1 a
+grep rule2 a
+
+: