Introducing a Sinatra app example

The purpose of this example is to demonstrate the potential of Resource
Registry declarative approach with a simple enough Sinatra application.

This exercise helps to make sure Resource Registry is abstract enough to
be used from a generic project.

examples/sinatra-pet-shelter/Gemfile

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+# frozen_string_literal: true
+
+source 'https://rubygems.org'
+
+gem 'json'
+gem 'sinatra'
+gem 'sinatra-contrib'
+
+group :development, :test do
+  gem 'pry'
+  gem 'rspec'
+end

examples/sinatra-pet-shelter/Gemfile.lock

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+GEM
+  remote: https://rubygems.org/
+  specs:
+    base64 (0.2.0)
+    coderay (1.1.3)
+    diff-lcs (1.5.1)
+    json (2.7.2)
+    method_source (1.1.0)
+    multi_json (1.15.0)
+    mustermann (3.0.3)
+      ruby2_keywords (~> 0.0.1)
+    pry (0.14.2)
+      coderay (~> 1.1)
+      method_source (~> 1.0)
+    rack (2.2.9)
+    rack-protection (3.2.0)
+      base64 (>= 0.1.0)
+      rack (~> 2.2, >= 2.2.4)
+    rspec (3.13.0)
+      rspec-core (~> 3.13.0)
+      rspec-expectations (~> 3.13.0)
+      rspec-mocks (~> 3.13.0)
+    rspec-core (3.13.1)
+      rspec-support (~> 3.13.0)
+    rspec-expectations (3.13.3)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-mocks (3.13.1)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-support (3.13.1)
+    ruby2_keywords (0.0.5)
+    sinatra (3.2.0)
+      mustermann (~> 3.0)
+      rack (~> 2.2, >= 2.2.4)
+      rack-protection (= 3.2.0)
+      tilt (~> 2.0)
+    sinatra-contrib (3.2.0)
+      multi_json (>= 0.0.2)
+      mustermann (~> 3.0)
+      rack-protection (= 3.2.0)
+      sinatra (= 3.2.0)
+      tilt (~> 2.0)
+    tilt (2.4.0)
+
+PLATFORMS
+  x86_64-linux
+
+DEPENDENCIES
+  json
+  pry
+  rspec
+  sinatra
+  sinatra-contrib
+
+BUNDLED WITH
+   2.4.7

examples/sinatra-pet-shelter/app.rb

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+# frozen_string_literal: true
+
+require 'sinatra'
+require 'sinatra/reloader' if development?
+
+# Main entrypoint of the application
+class App < Sinatra::Base
+  get '/' do
+    'Hello world!'
+  end
+end

examples/sinatra-pet-shelter/app_spec.rb

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+# frozen_string_literal: true
+
+require 'spec_helper'
+require_relative 'app'
+
+describe App do
+  it 'works' do
+    # ...
+  end
+end

examples/sinatra-pet-shelter/spec_helper.rb

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+# frozen_string_literal: true
+
+RSpec.configure do |config|
+end