Are you mocking me? (You should be) | Lupine Software Development

This post is just a friendly reminder for those that practice TDD/BDD to make sure they are not putting more ceremony into their tests than is necessary. Use mocks and stubs instead!

Mocks are just stand-ins that behave like the thing we want it to represent. Stubs will fake a method call and return a canned response. These save time both in setting up the test and in running it (depending on if your real objects are persisted in a test database). When you test a method you should only test things the method is actually doing.

I’m going to use Ruby on Rails and RSpec as an example. A classic situation is that we have an e-commerce application with a Order model that has many ShopItems. Now all we need to test that a cart object will calculate it’s total as the sum of the prices of all of its ShopItems. We don’t care what the names of the items are or if they are actually stored in the database.

describe Order do
  describe "#sub_total" do
    # writing everything to db
    it "should calculate the sum of all of its shop_items" do
      order = Order.create(some_options)
      3.times do
        order.shop_items << ShopItem.create(:price => 2.00)
      end
      order.subtotal.should be_within(0.01).of(6.0)
    end
    #  mocking
    it "should calculate the sum of all of its shop_items" do
      order = Order.create(some_options)
      fake_items = [stub(:price => 2.00), stub(:price => 2.00), stub(:price => 2.00)]
      order.stub!(:shop_items).and_return(fake_items)
      order.subtotal.should be_within(0.01).of(6.0)
    end
  end
end

Origninally posted on TechHui