Searching that way does not work in qt 5.5 (it was working in Qt 4.8.6):

QString text = "test";
QString pattern = "test";

QTextDocument document;
document.setPlainText( text );

QTextCursor cursor( &document );
cursor.setPosition( text.size(), QTextCursor::MoveAnchor );

cursor = document.find( pattern, cursor, QTextDocument::FindBackward );