Gist for my post "Rails: Model and Its Associated Testing"

create_users.rb

class CreateUsers < ActiveRecord::Migration
  def change
    create_table :users do |t|
      t.string :name
      t.string :email

      t.timestamps null: false
    end
  end
end

generate_user_model

rails g model User name:string email:string
      invoke  active_record
      create    db/migrate/20140724010738_create_users.rb
      create    app/models/user.rb
      invoke    test_unit
      create      test/models/user_test.rb
      create      test/fixtures/users.yml

schema.rb

ActiveRecord::Schema.define(version: 20150530101243) do

  create_table "users", force: :cascade do |t|
    t.string   "name"
    t.string   "email"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

end

user.rb

class User < ActiveRecord::Base
  #Some database adapters use case-sensitive indices, considering the
  #strings “Foo@ExAMPle.CoM” and “foo@example.com” to be distinct, but
  #our application treats those addresses as the same
  before_save {self.email = self.email.downcase}
  validates :name, presence: true, length: { maximum: 56 }
  # see http://www.rubular.com/ for regex parser
  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i
  validates :email, presence: true,
                    length: { maximum: 255 },
                    format: { with: VALID_EMAIL_REGEX },
                    uniqueness: { case_sensitive: false }

user_test.rb

require 'test_helper'

class UserTest < ActiveSupport::TestCase

  def setup
    @user = User.new(name: "Example User", email: "user@example.com")
  end

  test "should be valid" do
    assert @user.valid?
  end
end

user_test_v2.rb

require 'test_helper'

class UserTest < ActiveSupport::TestCase

  def setup
    @user = User.new(name: "Example User", email: "user@example.com")
  end

  test "should be valid" do
    assert @user.valid?
  end
  
  test "example user should be valid" do
    assert @user.valid?
  end

  test "name should be present" do
    @user.name = "       "
    assert_not @user.valid?
  end

  test "email should be present" do
    @user.email = "      "
    assert_not @user.valid?
  end

  test "name should not be too long" do
    @user.name = "long" * 20
    assert_not @user.valid?
  end

  # email
  test "email should not be too long" do
    @user.email = "long" * 70
    assert_not @user.valid?
  end

  test "email validation should accept valid email address" do
    valid_email_addresses = %w[user@gmail.com
                               User@foD.coM
                               A_user-d@x.com alice+bob@dd.cn
                               firtst.last@y.au]
    valid_email_addresses.each do |address|
      @user.email = address
      assert @user.valid?, "#{address} should be valid"
    end
  end

  test "email validation should not accept invalid email address" do
    invalid_email_addresses = %w[x.d@exx,com
                                 user.name@xample
                                 fag@example.
                                 foo@bar+x.com
                                 foo@bar_x.com]
    invalid_email_addresses.each do |address|
      @user.email = address
      assert_not @user.valid?, "#{address} should be invalid !"
    end
  end

  test "email address should be unique" do
    duplicated_user = @user.dup
    # the duplicate user has an email address that already exists in the database
    @user.save
    assert_not duplicated_user.valid?, "#{duplicated_user.email} already exists !"
  end