Why assert_select is not accepting parameters rails 4.2?

I am working on rails integration tests, someone wrote tests that were passing at that time but now they are giving warning

here is the line of code i was working on

assert_select "a[href=/monster_xml_users/#{user_xml.id}][data-method=delete]", I18n.t('revoke_access')

But now it is giving warning

Invalid CSS selector, Assertion not run

But if i write it alternatively like this

 assert_select "a", I18n.t('revoke_access')
        assert_select "a" do
          assert_select "[href=?]","/monster_xml_users/#{user_xml.id}"
          assert_select "[data-method=?]", "delete"
        end

Then it gives no warning and tests pass and it is correct. But i am unable to figure out why previous assertion is failing now ? Has assert_select syntax is changed now in Rails 4.2 ?