How to test your gem in a Rails application

Many gems in RubyGems require Rails to work as well and many of them are developed to use together with a Rails application like a plugin. How is known, the best way to ensure that some code is working as well is writing unit tests for it. But, for gems that depend or work together Rails, there is a nice way to test it into a Rails application, the name of it is Dummy tests.

The meaning of the word dummy is a kind of mannequin or replica of humans, but in ruby context, it's a kind of scope for you test your gem, in this case, a Rails application. I've added recently dummy tests in my gem rails-healthcheck in this pull request to check if this gem is rightly imported and have responded in success and failure cases as is waited.

These are the steps to add dummy tests into your gem using RSpec:

Create a Rails application into folder /spec:

rails new spec/dummy --skip-gemfile --skip-git --api

Require your gem in the dummy application:

A Rails application will require all gems into Gemfile's environments blocks using bundler, but, here we wanna test your local gem:

If your gem requires to run some setup, it's the moment to do it.

Add the gem rspec-rails as a development dependency:

Require dummy files and rspec-rails in tests:

Code your test:

For this example, my gem provides the method rgb_to_hex and it is used in the dummy's model Color. This model has the attributes red, green and blue.

Run rspec to test them:

rspec spec/color_spec.rb # or just rspec for all tests

# Color
#   #configure
#     with Dim Gray color
#       is expected to eq "3B3638"
#     with White Smoke color
#       is expected to eq "F9F7F7"
# Finished in 0.05234 seconds (files took 3.83 seconds to load)
# 2 examples, 0 failures

This example is so basic, but with dummy test you can test routes, controllers, helpers any what you want in a Rails application, for example, in the gem rails-healthcheck was tested all responses of Healthcheck::HealthcheckController#check mounted in the route /healthcheck or any route set in the initializer.

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