Create spec for model with joins associations - ruby-on-rails

Question

how can I do a spec for a model that calls the joins method
I have this code but not working i get errors for the method joins
def applicants_income_average
users.joins(:financial_data).sum(:net_income_verified) /
users.joins(:financial_data).where("financial_data.
net_income_verified IS NOT NULL").size
end
context "#applicants_income_average" do
before do
user_a.build_financial_data(net_income_verified: 12_000)
user_b.build_financial_data(net_income_verified: 13_000)
allow(whitelabel).to receive(:users).and_return([user_a, user_b])
allow(user_a).to receive(:join).and_return(user_a.financial_data)
allow(user_b).to receive(:join).and_return(user_b.financial_data)
end
it "Should return 12_500" do
expect(whitelabel.applicants_income_average).to eql(12_500)
end
end

Answer 1

Admittedly, it may be easier to test ActiveRecord through the database than it is to mock, thanks to ActiveRecord's method chaining. But, if you can put up with the chained allow statements, your tests will be SOOOO much faster if you mock ActiveRecord. Plus, you won't be testing something that has already been thoroughly tested by the Rails core team.
Here's how I would approach the problem above. I annotated some assumptions and modifications I made to the code. Hope it helps!
class Whitelabel
# I modified this for readability, but in the process discovered
# that the same query could probably be used for both the numerator
# and the denominator.
def applicants_income_average
sum_of_verified_net_income / count_of_users_with_verified_net_income
end
private
def sum_of_verified_net_income
users_with_verified_net_income.sum(:net_income_verified)
end
def count_of_users_with_verified_net_income
users_with_verified_net_income.size
end
# Using a single query and memoizing the results will improve performance
# This will also make it easier to test since we'll only call it once
def users_with_verified_net_income
#users_with_verified_net_income ||= do
users
.joins(:financial_data)
.where('financial_data.net_income_verified IS NOT NULL')
end
end
# I'm assuming this method must exist, given that the
# implementation of applicants_income_average referenced it
def users
User.where('some criteria')
end
end
describe Whitelabel do
subject(:whitelabel) { described_class.new }
describe '#applicants_income_average' do
subject(:applicants_income_average) { whitelabel.applicants_income_average }
let(:users) { instance_double('users') }
let(:users_with_financial_data) { instance_double('users_with_financial_data') }
let(:users_with_verified_net_income) do
instance_double('users_with_verified_net_income', sum: sum, size: size )
end
let(:sum) { 25000 }
let(:size) { 2 }
let(:average) { sum / size }
before do
allow(User).to receive(:where).and_return(users)
allow(users).to receive(:joins).and_return(users_with_financial_data)
allow(users_with_financial_data)
.to receive(:where)
.and_return(users_with_verified_net_income)
end
it 'selects the correct users' do
applicants_income_average
expect(User).to have_received(:where).with('some criteria')
end
it 'joins with financial data model' do
applicants_income_average
expect(users).to have_received(:joins).with(:financial_data)
end
it 'selects the users with verified net income' do
applicants_income_average
expect(users_with_financial_data)
.to have_received(:where)
.with('financial_data.net_income_verified IS NOT NULL')
end
it 'calculates average' do
expect(applicants_income_average).to eq(average)
end
end
end