Adding test for formatter

I have added database cleaner as for formatter spec it was trying to
use inbuild transactional fixture flag, which was failing as it
couldn't find any transaction to rollback. Hence switched to using
database_cleaner gem for using truncation as strategy

spec/swagger_rails/rspec/formatter_spec.rb

@@ -0,0 +1,79 @@
+require 'swagger_rails/rspec/formatter'
+require 'swagger_rails/rspec/dsl'
+require 'rails_helper'
+
+RSpec.describe ::SwaggerRails::RSpec::Formatter do
+  include FormatterSupport
+
+  def group
+    RSpec.describe('Ping API', swagger_doc: 'v1_api.json') do
+      path('/ping') do
+        post('checks if site is alive') do
+          consumes('application/json')
+          produces('application/json')
+          operation_description('A very long description')
+          response('200', '(OK) Site up and running') do
+            run_test!
+          end
+        end
+      end
+    end
+  end
+
+  def send_notification_for_all_child_groups(group)
+    send_notification :example_group_finished, group_notification(group)
+    group.children.each do |child|
+      return if child.class.name == 'ValidRequest'
+      send_notification_for_all_child_groups(child)
+    end
+  end
+
+  def swaggerize(*groups)
+    groups.each do |group|
+      group.run(reporter)
+      send_notification_for_all_child_groups group
+    end
+  end
+
+  before(:each) do
+    swagger_root = (Rails.root + 'swagger').to_s
+    SwaggerRails::Configuration.new.tap { |c| c.swagger_root = swagger_root }
+    allow(RSpec.configuration).to receive(:swagger_docs).and_return({ 'v1_api.json' => { swagger: '2.0',
+                                                                                         info: { title: 'API V1',
+                                                                                                 version: 'v1' } } })
+    allow(RSpec.configuration).to receive(:swagger_root).and_return(swagger_root)
+    @formatter = SwaggerRails::RSpec::Formatter.new(StringIO.new)
+  end
+
+  describe '#new' do
+    it 'should initialize the swagger_root' do
+      expect(@formatter.instance_variable_get(:@swagger_root)).to eq((Rails.root + 'swagger').to_s)
+      expect(@formatter.instance_variable_get(:@swagger_docs)).to eq({"v1_api.json"=>{:swagger=>"2.0", :info=>{:title=>"API V1", :version=>"v1"}}})
+    end
+  end
+
+  describe '#example_group_finished' do
+    before do
+      swaggerize(group)
+    end
+
+    it "should print 'Generating Swagger Docs ...'" do
+      expect(formatter_output.string).to eq("Generating Swagger Docs ...\n")
+    end
+
+    it 'should update the swagger_doc instance variable' do
+      expect(@formatter.instance_variable_get(:@swagger_docs)
+      ).to eq({
+                'v1_api.json' => { :swagger => '2.0',
+                                   :info => { :title => 'API V1',
+                                              :version => 'v1' },
+                                   :paths => { '/ping' => { :post => { :tags => ['Ping API'],
+                                                                        :summary => 'checks if site is alive',
+                                                                        :description => 'A very long description',
+                                                                        :consumes => ['application/json'],
+                                                                        :produces => ['application/json'],
+                                                                        :parameters => [],
+                                                                        :responses => { '200' => { :description => '(OK) Site up and running' } } } } } } })
+    end
+  end
+end