Rails: Testing named scopes with RSpec

Question

I am new to testing Rails web applications and RSpec. I work with legacy code and need to add tests. So what is the best way to test finders and named scopes with RSpec?

Answer 1

From https://coderwall.com/p/hc8ofa/testing-rails-model-default_scope-with-rspec

• no database queries
• no need to represent the query in a structure

Example:

class Trip < ActiveRecord::Base
  default_scope { order(departure: :asc) }
  ...
end

RSpec.describe Trip, type: :model do
  it "applies a default scope to collections by departure ascending" do
    expect(Trip.all.to_sql).to eq Trip.all.order(departure: :asc).to_sql
  end
end

Answer 2

David Chelimsky testing scopes (updated)

David Chelimsky example, (linked by Sam Peacey's comment), modernised.

# app/models/user.rb

class User < ActiveRecord::Base
  scope :admins, -> { where(admin: true) }
end

# spec/models/user_spec.rb

RSpec.describe User, type: :model do
  describe ".admins" do
    it "includes users with admin flag" do
      admin = User.create!(admin: true)
      expect(User.admins).to include(admin)
    end

    it "excludes users without admin flag" do
      non_admin = User.create(admin: false)
      expect(User.admins).not_to include(non_admin)
    end
  end
end

This produces a more 'spec-like' output (when using --format documentation):

User
  .admins
    includes users with admin flag
    excludes users without admin flag

Note about origination of this answer:

David Chelimsky, one of RSpec's creators, answered this question and Sam Peacey's link to it has more votes than the actual answer. The answer is not easy to find and follow as he is replying to someone and editing their answer in an email chain. This answer cleans that up and updates the RSpec code as, I guess, he would have written it today.

Answer 3

The creator of RSpec has recently blogged he thinks Validations are behavior, associations are structure. In other words he finds that associations (and scopes) should not nessesarily be tested directly. Tests for these will follow from the behavior you want.

In other words, current wisdom is that there is no need to test each scope directly, since you will cover these associations by testing the behavior of your application.

Answer 4

The problem with the first approach is that it actually queries the database. It is slow and unnecessary. If you don't mind, you can safely use the first approach. The second approach is fast and clear so I would recommend it.