Unable to perform password complexity implementation in Ruby on Rails?

I have researched a lot on this topic but due to some reason I am unable to perform password complexity implementation on my Ruby on Rails Web Application. I have installed the devise gem and followed Best flexible rails password security implementation and How to validate password strength with Devise in Ruby on Rails?.

My regex seems to be working when I check it online

/\A(?=.{8,})(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[[:^alnum:]])/x

but once I implement it inside my user.rb it just does not work.

My user.rb file:

#Active Record for Users
class User < ActiveRecord::Base
  belongs_to :entity
  has_and_belongs_to_many :groups, :join_table => "users_groups"
  has_many :surveys, inverse_of: :user
  has_many :results, inverse_of: :user

  validates :password, :firstName, :email, :salt, :role, :timezone, presence: true
  validates :email, :uniqueness => {:scope => :entity_id}
  validates_format_of :email, :with => /.+@.+\..+/i

  devise :database_authenticatable, :validatable
  validate :password_complexity

  #User Authentication
  def self.authenticate(email="", lpassword="")
    users = User.where(email: email)
    results = []
    users.each do |user|
      if user && user.match_password(lpassword)
      results.push(user)
      end
    end
    if(results.length == 0)
    return false
    else
    return results
    end
  end

  #Password Check
  def match_password(lpassword="")
        return (BCrypt::Password.new(password).is_password?(lpassword+salt))
    end

  #Password Authentication
  def password_complexity
      if password.present? and not password.match(/\A(?=.{8,})(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[[:^alnum:]])/x)
        errors.add :password, "must include at least one lowercase letter, one uppercase letter, and one digit"
      end
   end

end