Question

How can I write an Rspec test for the following? Using TDD, I want to be able to write a test to that requires the following code in order to pass.

class AddEmailUniquenessIndex < ActiveRecord::Migration
  def up
    add_index :users, :email, :unqiue => true
  end

  def down
    remove_index :users, :email
  end
end

Answer 1

Within your test, just try to create two users with same e-mail address. Second one should not have valid email. Something like this:

it "prevents duplicates" do
  user1 = create(:user, email: '[e-mail]')
  user2 = build(:user, email: '[e-mail]')

  user1.should be_valid
  user2.should_not have_valid(:email)
end

Note that I’m using factory_girl and valid_attribute gems in the example above.
I’m also assuming that you have validates :email, uniqueness: true in your model.