API to assert List<WidgetSelector>

[passsy]

Sometimes I want to assert multiple widgets with the same condition. e.g. when building a form.
I could write it multi-line, but it might be useful to assert all at the same time

final WidgetSelector<Checkbox> boxA = spotCheckboxA();
final WidgetSelector<Checkbox> boxB = spotCheckboxB();
final WidgetSelector<Checkbox> boxC = spotCheckboxC();

// assert that those widgets are checked
// [boxA, boxB, boxC].areChecked();