message_detail.rb

class MessageDetail

  include ActiveModel::Validations

  attr_accessor :body, :length

  validates :body, presence: true, length: { minimum: 1 }
  validates :length, presence: true, :numericality => {:greater_than => 0}

  def initialize(body,length)
    @body = body
    @length = length
  end

  def self.build(body,length)
    message_detail = self.new(body,length)

    if message_detail.valid? == false
      raise StandardError, "Invalid Message Detail Passed"
    end

    return message_detail
  end

end

is build reserved in terms of rspec. From inside my rspec tests, after some painful debugging i realized that my build function never ran and i always got nil as return value.