How to make selection on ExtJS Combo Box with Bryntum Siesta Test?

I've a datatable form and includes several items such as textfield, datefield and combobox. How i'll be able to make selection items with Siesta for combobox and I need to set Siesta waiting time more than 30000ms because data is loading through ajax request to combobox.

There is a snippet I've used which has been failed;

t.it('Should create a new registration', function (t) {
        t.chain(
            {click: '>> button[text=New]'},
            {waitForCQ: 'regdata[title=New Registration]'},
            {click: '>> firstnamefld[xtype=firstnamefld]'},
            {type: 'Siesta Reg', target: '>> firstnamefld[xtype=firstnamefld]'},
            {click: '>> lastnamefld[xtype=lastnamefld]'},
            {type: 'Test One', target: '>> lastnamefld[xtype=lastnamefld]'},
            {click: '>> datefld[xtype=datefld]'},
            {type: '11.10.2017', target: '>> checkinfld[xtype=checkinfld]'}, //Probably that's not correct way to choose date on datefield but it works

//Here is making ajax request to load data in combo.but Siesta isn't waiting for selection.
//I shouldn't use 'type' for this part but I couldn't find any proper property.
                {click: '>> groupcombo[xtype=groupcombo]'},
                {type: 'Group One', target: '>> groupcombo[xtype=groupcombo]'}