Testing Active Record Integration in Ruby Gems
When I was writing the expiry calculator gem (extracted from a license management system), the library’s main logic has some sort of integration with ActiveRecord, and I needed to verify that the easy way.
Mocking the built-in active record connection pool and tables mapping showed to be cumbersome and may not ideally allow to validate the intended behaviour. Luckily, I found pieces in SO and Github to do the unit testing in few simple steps, with on the fly db (Sqlite). I have put it together in the following guide, polished for Rspec with ad-hoc migration methods.
Steps
1) Adding the required libraries in the dev group of our Gem spec file.
Gem::Specification.new do |spec|
# ..
spec.add_development_dependency "activerecord", "~> 7"
spec.add_development_dependency "sqlite3", "~> 2"
end
2. The db setup logic is extracted in a helper.
Replace posts with your intended model with the attributes (columns) you need.
# spec/support/db_helper.rb
module TestDbHelper
def establish_coonection
ActiveRecord::Base.establish_connection adapter: "sqlite3", database: ":memory:"
end
def up
ActiveRecord::Base.connection.create_table :posts do |t|
t.integer :name
t.date :ends_at
t.timestamps
end
end
def down
ActiveRecord::Base.connection.drop_table :posts
end
end
3. For convenience, I mixed in the helper in the example and example group classes of rspec.
require "support/db_helper"
RSpec.configure do |config|
# ...
config.include TestDbHelper
config.extend TestDbHelper
end
4. Then, we invoke the db functions.
Also we build an anonymous model in let statements.
RSpec.describe MyGemClass do
# ...
context "Arguments" do
establish_coonection
before { up }
after { down }
let(:model_class) do
Class.new(ActiveRecord::Base) { self.table_name = "posts" }
end
let(:model) { model_class.new(ends_at: Date.today + 10) }
end
end
5. Lastly, we use the model to test against in our case (calculate here).
it "supports active_record parameter with attr accessor" do
expect(subject.calculate(model, :ends_at)).to eq(10)
end
Done.
