Instead of removing group separators after conversion, we can omit them using QLocale. The decimal point and group separators can be the same character, if the user configures the system locale accordingly. Add a test that compares the text shown by the spinbox with what the locale would do. Since the C locale sets the OmitGroupSeperator number option by default, cover several cases to verify that we explicitly set the correct number options based on the QDoubleSpinBox property, and implement a customized system locale that returns the same character for group separator and decimal point. Fixes: QTBUG-77939 Pick-to: 6.8 Change-Id: I257ea44ed988c70cb4fc0cfc81c3b366c0a431eb Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>