Setting FactoryGirl and use it in Grape and RSpec?

In my Grape ruby project. I'm separating my models to a gem so I can use it between my ruby projects.

Now the problem is that with my activerecords, let's say I'm dealing with User model, now it looks something like this:

module MyApp
  module Core    
    class User < ActiveRecord::Base
      self.table_name = 'users'          
    end    
  end
end

And I'm using Factory girl something like this:

FactoryGirl.define do
  factory :user do

    first_name { Faker::Name.first_name }
    last_name { Faker::Name.last_name }
    email { Faker::Internet.email }
    password { "12345678" }
    password_confirmation { "12345678" }
  end
end

And let's say I have the following rspec test:

require 'spec_helper'

describe MyApp::Core::User do
    it "has name assigned" do
      user = build(:member, first_name: 'Eki', last_name: 'Eqbal')
      expect(user.first_name).to eq('Eki')
      expect(user.last_name).to eq('Eqbal')
    end  
end

And when I try to run the test:

⇒  bundle exec rspec spec/unit/users_spec.rb
warning: parser/current is loading parser/ruby22, which recognizes
warning: 2.2.3-compliant syntax, but you are running 2.2.0.
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}
F

Failures:

  1) MyApp::Core::User has name assigned
     Failure/Error: user = build(:user, first_name: 'Eki', last_name: 'Eqbal')
     NameError:
       uninitialized constant User
     # ./spec/unit/users_spec.rb:37:in `block (2 levels) in <top (required)>'

Finished in 0.14788 seconds
1 example, 1 failure

Failed examples: