Strange. Can you confirm the alerts you get when using below code.

var wsOptions4 = 'BR';
 var identifer = g_form.getValue('current_shift_identifier');
alert('Identifier'+identifer);
 if (identifer.substring(0,2)==wsOptions4) {
alert('inside loop');
 g_form.setVisible('test',true);//true,false to show/hide
}