tests: add date printing and parsing tests

Until now, there was no coverage of relative date printing
or approxidate parsing routines (mainly because we had no
way of faking the "now" time for relative date calculations,
which made consistent testing impossible).

This new script tries to exercise the basic features of
show_date and approxidate. Most of the tests are just "this
obvious thing works" to prevent future regressions, with a
few exceptions:

  - We confirm the fix in 607a9e8a that relative year/month
    dates in the latter half of a year round correctly.

  - We confirm that the improvements in b5373e9 and 1bddb25
    work.

  - A few tests are marked to expect failure, which are
    regressions recently introduced by the two commits
    above.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t0006-date.sh

+#!/bin/sh
+
+test_description='test date parsing and printing'
+. ./test-lib.sh
+
+# arbitrary reference time: 2009-08-30 19:20:00
+TEST_DATE_NOW=1251660000; export TEST_DATE_NOW
+
+check_show() {
+	t=$(($TEST_DATE_NOW - $1))
+	echo "$t -> $2" >expect
+	test_expect_${3:-success} "relative date ($2)" "
+	test-date show $t >actual &&
+	test_cmp expect actual
+	"
+}
+
+check_show 5 '5 seconds ago'
+check_show 300 '5 minutes ago'
+check_show 18000 '5 hours ago'
+check_show 432000 '5 days ago'
+check_show 1728000 '3 weeks ago'
+check_show 13000000 '5 months ago'
+check_show 37500000 '1 year, 2 months ago'
+check_show 55188000 '1 year, 9 months ago'
+check_show 630000000 '20 years ago'
+
+check_parse() {
+	echo "$1 -> $2" >expect
+	test_expect_${3:-success} "parse date ($1)" "
+	test-date parse '$1' >actual &&
+	test_cmp expect actual
+	"
+}
+
+check_parse 2008 bad
+check_parse 2008-02 bad
+check_parse 2008-02-14 bad
+check_parse '2008-02-14 20:30:45' '2008-02-14 20:30:45 +0000'
+
+check_approxidate() {
+	echo "$1 -> $2 +0000" >expect
+	test_expect_${3:-success} "parse approxidate ($1)" "
+	test-date approxidate '$1' >actual &&
+	test_cmp expect actual
+	"
+}
+
+check_approxidate now '2009-08-30 19:20:00'
+check_approxidate '5 seconds ago' '2009-08-30 19:19:55'
+check_approxidate 5.seconds.ago '2009-08-30 19:19:55'
+check_approxidate 10.minutes.ago '2009-08-30 19:10:00'
+check_approxidate yesterday '2009-08-29 19:20:00'
+check_approxidate 3.days.ago '2009-08-27 19:20:00'
+check_approxidate 3.weeks.ago '2009-08-09 19:20:00'
+check_approxidate 3.months.ago '2009-05-30 19:20:00' failure
+check_approxidate 2.years.3.months.ago '2007-05-30 19:20:00' failure
+
+check_approxidate '6am yesterday' '2009-08-29 06:00:00'
+check_approxidate '6pm yesterday' '2009-08-29 18:00:00'
+check_approxidate '3:00' '2009-08-30 03:00:00'
+check_approxidate '15:00' '2009-08-30 15:00:00'
+check_approxidate 'noon today' '2009-08-30 12:00:00'
+check_approxidate 'noon yesterday' '2009-08-29 12:00:00'
+
+check_approxidate 'last tuesday' '2009-08-25 19:20:00'
+check_approxidate 'July 5th' '2009-07-05 19:20:00'
+check_approxidate '06/05/2009' '2009-06-05 19:20:00'
+check_approxidate '06.05.2009' '2009-05-06 19:20:00'
+
+check_approxidate 'Jun 6, 5AM' '2009-06-06 05:00:00'
+check_approxidate '5AM Jun 6' '2009-06-06 05:00:00'
+check_approxidate '6AM, June 7, 2009' '2009-06-07 06:00:00'
+
+test_done