test-lib: introduce API for verifying file mtime

Add functions `test_set_magic_mtime` and `test_is_magic_mtime` which can
be used to (re)set the mtime of a file to a predefined ("magic")
timestamp, then perform some operations and finally check for mtime
changes of the file.

The core implementation follows the suggestion from the
mailing list [1].

[1] https://lore.kernel.org/git/xmqqczl5hpaq.fsf@gitster.g/T/#u

Signed-off-by: Marc Strapetz <marc.strapetz@syntevo.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 389153e591620a379ebe496026eaa05db8ac8dc2..c1afa0884bfd743bb6b523af3beb6844561682fa 100644 (file)
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1806,3 +1806,36 @@ test_region () {
 test_readlink () {
        perl -le 'print readlink($_) for @ARGV' "$@"
 }
+
+# Set mtime to a fixed "magic" timestamp in mid February 2009, before we
+# run an operation that may or may not touch the file.  If the file was
+# touched, its timestamp will not accidentally have such an old timestamp,
+# as long as your filesystem clock is reasonably correct.  To verify the
+# timestamp, follow up with test_is_magic_mtime.
+#
+# An optional increment to the magic timestamp may be specified as second
+# argument.
+test_set_magic_mtime () {
+       local inc=${2:-0} &&
+       local mtime=$((1234567890 + $inc)) &&
+       test-tool chmtime =$mtime "$1" &&
+       test_is_magic_mtime "$1" $inc
+}
+
+# Test whether the given file has the "magic" mtime set.  This is meant to
+# be used in combination with test_set_magic_mtime.
+#
+# An optional increment to the magic timestamp may be specified as second
+# argument.  Usually, this should be the same increment which was used for
+# the associated test_set_magic_mtime.
+test_is_magic_mtime () {
+       local inc=${2:-0} &&
+       local mtime=$((1234567890 + $inc)) &&
+       echo $mtime >.git/test-mtime-expect &&
+       test-tool chmtime --get "$1" >.git/test-mtime-actual &&
+       test_cmp .git/test-mtime-expect .git/test-mtime-actual
+       local ret=$?
+       rm -f .git/test-mtime-expect
+       rm -f .git/test-mtime-actual
+       return $ret
+}