On Chapter 7, Excercise 2, of Michael Hartl's (excellent) Rails Tutorial

Question

Exercise 2: His suggested template for checking error messages associated with signing up on a form are the last two assert_selects below:

require 'test_helper'

class UsersSignupTest < ActionDispatch::IntegrationTest

  test "invalid signup information" do
    get signup_path
    assert_no_difference 'User.count' do
      post users_path, user: { name:  "",
                               email: "user@invalid",
                               password:              "foo",
                               password_confirmation: "bar" }
    end
    assert_template 'users/new'
    assert_select 'div#<CSS id for error explanation>'
    assert_select 'div.<CSS class for field with error>'
  end

I cannot figure out what needs to replace what he has within the brackets. The custom CSS has form sections like this:

#error_explanation {
  color: red;
  ul {
    color: red;
    margin: 0 0 30px 0;
  }
}

.field_with_errors {
  @extend .has-error;
  .form-control {
    color: $state-danger-text;
  }
}

Answer 1

add them as he gave instructions

  assert_select 'div#<CSS id for error explanation>'
  assert_select 'div.<CSS class for field with error>'

will be

  assert_select 'div#error_explanation'
  assert_select 'div.field_with_errors'

Answer 2

assert_select 'div#error_explanation'
assert_select 'div.field_with_errors'

The tutorial wanted me to replace the example with above code. I did not understand that, but at last found the answer.