public function testMakeFieldReadonly()
{
$FieldList = new FieldList(new TabSet('Root', new Tab('Main', new TextField('A'), new TextField('B'))));
$FieldList->makeFieldReadonly('A');
$this->assertTrue($FieldList->dataFieldByName('A')->isReadonly(), 'Field nested inside a TabSet and FieldList can be marked readonly by FieldList->makeFieldReadonly()');
}