Sort out an anomaly in tst_QDateTime::springForward()

It noted that an unspecified function claimed the offset it was
checking should be +1, while testing it against that or -1. The
function turns out to be QDateTime::addDays(), whose doc did indeed,
misleadingly, say that it lands after a gap it would have hit. It in
fact overshoots the gap in the direction of its change. Amend its
docs, likewise those of addMonths() and addYears(), to reflect the
true behavior.

Amend the test to look at the direction of the step its taking and
anticipate that the adjustment will be in the same direction; then
compare the actual adjustment to that.

Change-Id: I9ab918fac0ab2195ef014983f37fccc435bf0498
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

0 files changed, 0 insertions, 0 deletions