Confused with Rails 4 format validation [RESOLVED]

Hi. I'm confused with my tests failing on profile name validation (I'm going through Build A Simple Ruby on Rails application, but using Rails 4, not 3.2 as in the videos).

My problem is I've got this validator of profile_name:

  validates :profile_name,
            presence: true,
            uniqueness: true,
            format: {
              with: /\A[a-zA-Z0-9_\-]+\z/,
              message: "must be formatted correctly"
            }

And the following test fails:

  test "a user can have a correctly formatted profile name" do
    user = User.new(first_name: "Kirill",
                    last_name: "Kovalchuk",
                    email: "the.nemoden@gmail.com")
    user.password = user.password_confirmation = "qwerty1234"
    user.profile_name = "nemoden_1"
    assert user.valid?
  end

As the documatation says it's not safe to use ^ and $ since $ matches \n (new-line characted) which makes sense since I don't want people to have a possibility to enter an email like "john_doe@johndoeswebsite.com\n< script>/* guess who stole your cookies? */< /script >"

And the official documentation uses \A and \z in the examples here.

I don't wanna go with multiline option just to make test pass and then I'm using ^ and $ test don't pass either, it says:

<blockquote> The provided regular expression is using multiline anchors (^ or $), which may present a security risk. Did you mean to use \A and \z, or forgot to add the :multiline => true option? (ArgumentError)</blockquote>

If I use IRB, it tests my profile name correctly:

$ irb
1.9.3p484 :002 > /\A[a-zA-Z0-9_\-]+\z/.match('nemoden_1')
 => #<MatchData "nemoden_1">