Rspec model tests for average rating method

Question

I'm trying to write tests for the following method:

def average_rating
  reviews = self.reviews
  review_sum = reviews.inject(0) { |sum, review| sum += review.rating }
  avg_rating = (review_sum / reviews.count).to_i unless review_sum == 0
end

Here's what I have so far:

describe "#average_rating" do
it "should be nil when there are no reviews" do
  api_without_reviews = Api.new name: 'Fake API', description: 'It does something', category: 'Fake category', url: 'http://www.example.com'
  api_without_reviews.average_rating.should be_nil
end
it "should calculate average rating properly" do
  api_with_reviews = Api.new name: 'Fake API', description: 'It does something', category: 'Fake category', url: 'http://www.example.com'
  api_with_reviews.save
  api_with_reviews.reviews.create rating: Random.rand(1..5), thoughts: 'blah'
  api_with_reviews.reviews.create rating: Random.rand(1..5), thoughts: 'blah'
  average = api_with_reviews.reviews.inject(0) { |sum, review| sum += review.rating } / api_with_reviews.reviews.count
  api_with_reviews.average_rating.should eq average
end

end

How can I test that the review_sum variable is calculating the sum correctly, or is the method already fully tested? I'm new at rspec so any help is appreciated!

Answer 1

To answer directly I suggest you not to:

• Generate random value of the review rating
• Copy the method code directly to verify it. You can't score your own paper, don't you?

Instead:

• Use manually created ratings and calculate the average manually
• Verify if the method could output what you've calculated.

Further improvement

• Use FactoryGirl to create test objects.
• DRY the code

My version(assume FactoryGirl installed)

describe "API" do
  describe "average_rating" do
    # Use "before" but not "let" because this var must be clean in every example
    before { @api = FactoryGirl.create(:api) }
  
    it "should be nil when there are no reviews" do
      @api.average_rating.should be_nil
    end

    it "should calculate average rating properly" do
      [1, 5].each do |r|
        FactoryGirl.create(:review, rating: r, api: @api)
      end 
      @api.average_rating.should eq(3)
    end
  end
end

# spec/factories.rb
FactoryGirl.define do
  factory :api do
    name 'Fake API'
    description 'It does something'
    category 'Fake category'
    url 'http://www.example.com'
  end

  factory :review do
    rating rand(1..5)
    thoughts "blah"
    api   #Association: belongs_to API
  end
end