Unit test for a command class

I have a command class for the export button that i wan to test it whit automation unit test.

void ICommand.Execute(object parameter)
        {
            string FileName = "";
            if (measurementViewModel.NavigationResolver.ShowSaveFileDialog(ref FileName))
            {
                bool IsFirstMasurement = true;
                foreach (Measurement measurement in measurementViewModel.Measurements)
                {
                    if (measurement.IsSelected)
                    {
                        if (IsFirstMasurement)
                        {
                            measurementViewModel.MeasurementModel.ExportMeasurementToXml(FileName, measurement);

                            IsFirstMasurement = false;
                        }
                        else
                            measurementViewModel.MeasurementModel.AppendMeasurementsToXml(FileName, measurement);
                    }
                }
                measurementViewModel.Measurements.MoveCurrentToPosition(-1);
                measurementViewModel.Measurements.Refresh();
            }
        }

I want to test if 1 measurement are selected in the measurement list how measurement export will be exported with export function and if i select 3 measurement from the list, if the export function will export 3 measurement not the hole list of measurement. I want to focus more on that measurement.is selected function. Any suggestion are welcome.