Click cell widget button

spec.js

it('should click button widget in 3rd row', function () {
    // fill in password field 
    ST.textField('[fieldLabel=Password]').type('a');
    // click login button
    ST.button('[text=Login]').click();
    // do actions on Project Members grid
    ST
        .grid('[title^=Project Members]')
        .rowAt(2) // get third row
        .down('.x-btn') // traverse dom hierarchy to choose correct button
        .click(); // click it!
});

target.js

http://examples.sencha.com/extjs/6.5.0/examples/classic/ticket-app/index.html