Make the comment to be the answer.
The possible reason for the problem is that you send the mouse event to the parent widget rather then to the button itself. What if you try to find your button by using QWidget::childAt()
function? For example:
[..]
QTest::mouseMove ( myWidget, QPoint( 70, 100 ), -1 );
QWidget *btn = myWidget->childAt(70, 100);
if (btn) {
QTest::mouseClick ( btn, Qt::LeftButton, Qt::NoModifier, QPoint( 70, 100 ), 100);
}