Using this step definition you can check if any form field (text field, checkbox, etc) or button is disabled:
Then the "Name" field should be disabled
And the "Save" button should be disabled
But the "Locked" field should not be disabled
This step part of Spreewald Show archive.org snapshot .
Then /^"([^\"]*)" should( not)? be disabled$/ do |label, negate|
attributes = field_labeled(label).element.attributes.keys
attributes.send(negate ? :should_not : :should, include('disabled'))
end