[glib] tests: Use a different time for testing UNIX timestamps

[Philip Withnall <pwithnall src gnome org>]

commit 4183cedbe26ee14e84c4360a341fd518e3a11eb9
Author: Philip Withnall <withnall endlessm com>
Date:   Fri Feb 9 14:01:01 2018 +0000

    tests: Use a different time for testing UNIX timestamps
    
    The test_GDateTime_new_from_unix() test creates a UNIX timestamp
    representing 1990-01-01 00:00:00 in the local timezone, and then turns
    it into a GDateTime using g_date_time_new_from_unix_local(). This should
    succeed regardless of the current local timezone (TZ environment
    variable).
    
    However, it was failing for TZ=America/Lima, and *only* for that
    timezone.
    
    As it turns out, Lima used to have a DST leap at exactly 00:00:00 on the
    1st of January — but this stopped in 1994, which made investigation a
    bit harder. See:
    https://www.timeanddate.com/time/change/peru/lima?year=1990.
    
    What was happening is that 1990-01-01 00:00:00 was being converted to
    the timestamp 631170000, but GDateTime was converting that timestamp to
    1990-01-01 01:00:00 when loading it. Both conversions are correct: a DST
    leap creates an equivalence between an hour’s worth of timestamps.
    
    We can somewhat validate this by seeing that timestamp 631169999 maps to
    1989-12-31 23:59:59, and timestamp 631170001 maps to 1990-01-01
    01:00:01.
    
    Fix this by changing the date used by the test to one where no timezone
    was undergoing a DST leap in 1990. This should never change, as all that
    data is now historical.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>
    
    https://bugzilla.gnome.org/show_bug.cgi?id=793319

 glib/tests/gdatetime.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/glib/tests/gdatetime.c b/glib/tests/gdatetime.c
index 296a1e905..f22f64654 100644
--- a/glib/tests/gdatetime.c
+++ b/glib/tests/gdatetime.c
@@ -122,11 +122,14 @@ test_GDateTime_new_from_unix (void)
   g_assert_cmpint (g_date_time_get_second (dt), ==, tm.tm_sec);
   g_date_time_unref (dt);
 
+  /* Choose 1990-01-01 04:00:00 because no DST leaps happened then. The more
+   * obvious 1990-01-01 00:00:00 was a DST leap in America/Lima (which has,
+   * confusingly, since stopped using DST). */
   memset (&tm, 0, sizeof (tm));
   tm.tm_year = 90;
   tm.tm_mday = 1;
   tm.tm_mon = 0;
-  tm.tm_hour = 0;
+  tm.tm_hour = 4;
   tm.tm_min = 0;
   tm.tm_sec = 0;
   tm.tm_isdst = -1;
@@ -136,7 +139,7 @@ test_GDateTime_new_from_unix (void)
   g_assert_cmpint (g_date_time_get_year (dt), ==, 1990);
   g_assert_cmpint (g_date_time_get_month (dt), ==, 1);
   g_assert_cmpint (g_date_time_get_day_of_month (dt), ==, 1);
-  g_assert_cmpint (g_date_time_get_hour (dt), ==, 0);
+  g_assert_cmpint (g_date_time_get_hour (dt), ==, 4);
   g_assert_cmpint (g_date_time_get_minute (dt), ==, 0);
   g_assert_cmpint (g_date_time_get_second (dt), ==, 0);
   g_date_time_unref (dt);