Sinatra applications with RSpec
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There are times when the only thing I want to create is a simple API. In the Ruby ecosystem the standard for creating something simple is Sinatra. But, there are a lot of things you miss in Sinatra that you have predefined in Rails. Sinatra let’s you define and include only the things you actually need. Maybe this is a good thing, maybe it is not.
However, the things you need for a complete Sinatra application are sometimes hard to include. This tutorial aims to help you in that process, by showing you how to create a simple Sinatra web application that uses RSpec for testing.
We will create a simple Todo application with only two actions. One for listing all the existing Todos and another one for adding a new one. It will use Sinatra for creating the API, RSpec for testing, and it will also include Active Support for adding a couple of nice functionality to the Ruby language.
So let’s begin! The first thing is to create a Gemfile and list all the dependencies. From the above description of the project we can simply deduct all the things that are necessary.
source "https://rubygems.org" gem "rack" gem "sinatra" gem "activesupport" group :test do gem "rspec" gem "rack-test" end
We can install the dependencies with
bundle install. I like to put my dependencies in the
vendor/bundle directory. With that the command becomes the following
bundle install --path vendor/bundle
Then we can initialize RSpec in for project. The following command should create an
.rspec and a
bundle exec rspec --init
As an old Rails habit, I like to have two folders in my project.
app for containing all the application specific files.
config for the project’s configuration
Let’s create them:
mkdir app mkdir config
In this example project I will have only one configuration file called
config/environment.rb. This file will be responsible for booting up the application and loading all the gems from Bundler. Also it will load and set up active support for this project.
Instead of using a database, this simple API will use only a global variable named
$db. This is for the sake of simplicity and should be replaced with a real database.
With the above description we can implement that file like this
require "rubygems" require "bundler" Bundler.require(:default) # load all the default gems Bundler.require(Sinatra::Base.environment) # load all the environment specific gems require "active_support/deprecation" require "active_support/all" $db =  # a fake database
Now we should make the spec_helper load this file before the tests are run. To do that we need to prepend that file with a require statement.
While we are here it would also be a good idea to set the environment to test when running RSpec, include some rake test helpers, and clear the fake database before each test.
spec/spec_helper.rb file should look similar to this.
ENV['RACK_ENV'] = 'test' require "./config/environment" RSpec.configure do |config| config.include Rack::Test::Methods config.before(:each) do $db =  end config.expect_with :rspec do |expectations| expectations.include_chain_clauses_in_custom_matcher_descriptions = true end config.mock_with :rspec do |mocks| mocks.verify_partial_doubles = true end config.filter_run :focus config.run_all_when_everything_filtered = true config.disable_monkey_patching! config.warnings = true if config.files_to_run.one? config.default_formatter = 'doc' end config.profile_examples = 10 config.order = :random Kernel.srand config.seed end
As a good TDD abiding citizen we should write some test for our Todo application before actually implementing the code.
touch app/todo_api.rb touch spec/app/todo_api_spec.rb
and describe the application in your test file
require "spec_helper" RSpec.describe TodoApi do def app TodoApi # this defines the active application for this test end end
and then a matching class in the app file
class TodoApi < Sinatra::Base end
Then we should create a get action for listing all the todos in the system. Such a get request should return nothing if the database is empty and a list of todos if the contains several todos
describe "GET todos" do context "no todos" do it "returns no todo" do get "/" expect(last_response.body).to eq("") expect(last_response.status).to eq 200 end end context "several todos" do before do @todos = ["hello", "world", "!"] $db = @todos end it "returns all the todos" do get "/" expect(last_response.body).to eq @todos.join("\n") expect(last_response.status).to eq 200 end end end
A matching implementation would be
get "/" do $db.join("\n") end
Creating a new todo is also simple. The todo message should be passed as an argument to the POST action.
describe "POST todo" do it "returns status 200" do post "/", :todo => "hello rspec" expect(last_response.status).to eq 200 end context "todo param missing" do it "returns status 400" do post "/" expect(last_response.status).to eq 400 end end end
post "/" do return 400 unless params["todo"].present? $db << params["todo"] 200 end
Making rack happy and running the App
In order to run your application with the
we should create an
config.ru file with the following content
require "./config/environment" run Rack::URLMap.new("/" => TodoApi)
and run our application with
bundle exec rackup config.ru
Hooray! Our simple API is finished.
Read the full source code in this GitHub repository.