Add spec for user model

spec/factories/users.rb

@@ -1,6 +1,6 @@
 FactoryGirl.define do
   factory :user do
     email "test@example.com"
-    password_digest ""
+    password_digest "password"
   end
 end

spec/models/user_spec.rb

@@ -1,5 +1,13 @@
-require 'rails_helper'
+require 'spec_helper'
 
 RSpec.describe User, type: :model do
-  pending "add some examples to (or delete) #{__FILE__}"
+  it { is_expected.to validate_presence_of(:email) }
+  it { is_expected.to validate_presence_of(:password_digest) }
+
+  it 'validates uniqueness of email' do
+    create(:user, email: 'test@example.com')
+    user = User.new(email: 'test@example.com')
+
+    expect(user).to validate_uniqueness_of(:email)
+  end
 end