RSpec unit testing an eigenclass: undefined method

Question

I'm trying to test the method cumulative_cost in my Product model.

#app/models/product.rb
class Product < ActiveRecord::Base
  class << self
    def cumulative_cost
      self.sum(:cost)
    end
  end
end

So I'll run something like Product.where(name:"surfboard").cumulative_cost Let's say it returns two records, one with a cost of 1000, and another of 150, it'll return => 1150.

So here's what I've written as a test.

RSpec.describe Product, "class << self#cumulative_cost" do
  it "should return the total cost of a collection of products"
    products = Product.create!([{name:"surfboard", cost:1000}, {name:"surfboard", cost:150}])
    expect(products.cumulative_cost).to eq(1150)
  end
end

Then when I run my test, it fails.

undefined method `cumulative_cost' for #<Array:0x007fe3e31844e8>

Any help would be greatly appreciated.

I can't believe someone would vote this amazing question down, anonymously!!! True troll form. — thedanotto, Aug 31 '15 at 22:24

K M Rakibul Islam · Answer 1 · 2015-08-31T22:11:31.620

2

cumulative_cost is a class method on Product model. So, you have to call it like: Product.cumulative_cost.

The error is saying:

undefined method `cumulative_cost' for #<Array:0x007fe3e31844e8>

which means, you are calling this cumulative_cost method on an array but it's not implemented on array objects, hence it's getting this error.

Change your expectation to: (according to SteveTurczyn's answer)

expect(Product.where(name:"surfboard").cumulative_cost).to eq(1150)

edited Aug 31 '15 at 22:11

answered Aug 31 '15 at 22:03

K M Rakibul Islam

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Ok, I get that. Why isn't it a collection of ActiveRecord Objects? And how do I create these two buildings as a collection? – thedanotto Aug 31 '15 at 22:05
You are calling `create!` method on `Product` with an array param, so it reutns an array back to the `products`. Use this: `expect(Product.where(name:"surfboard").cumulative_cost).to eq(1150)` – K M Rakibul Islam Aug 31 '15 at 22:16
1

It's a team effort. :) – SteveTurczyn Sep 01 '15 at 08:36

score 2 · Accepted Answer · answered Aug 31 '15 at 22:08

2

Following on from K M Rakbul Islam's answer...

products is an array because that's what Product.create! with a supplied array returns.

Your test should be...

expect(Product.where(name:"surfboard").cumulative_cost).to eq(1150)

answered Aug 31 '15 at 22:08

SteveTurczyn

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Yes, SteveTurczyn deserves it :-) I spent more time explaining the problem before giving the correct answer :P – K M Rakibul Islam Aug 31 '15 at 22:27
SteveTurczyn, one +1 from me too :) – K M Rakibul Islam Aug 31 '15 at 22:30

RSpec unit testing an eigenclass: undefined method

2 Answers2