I guess you have to get pretty unlucky to hit this

# GLib:ERROR:/«PKGBUILDDIR»/./glib/tests/gdatetime.c:674:test_GDateTime_now_utc: assertion failed (tm.tm_sec == g_date_time_get_second (dt)): (37 == 38)

static void
test_GDateTime_now_utc (void)
{
  GDateTime *dt;
  time_t     t;
  struct tm  tm;

  t = time (NULL);
  gmtime_r (&t, &tm);
  /* … */
  /* Here we get interrupted long enough for the second to tick over */
  dt = g_date_time_new_now_utc ();
  /* … */
  g_assert_cmpint (tm.tm_sec, ==, g_date_time_get_second (dt));
  g_date_time_unref (dt);
}