Add yaml support (#7)

rswag-specs/spec/rswag/specs/swagger_formatter_spec.rb

@@ -55,14 +55,31 @@ module OpenApi
                 'v1/swagger.json' => { info: { version: 'v1' } },
                 'v2/swagger.json' => { info: { version: 'v2' } }
             )
+            allow(config).to receive(:swagger_format).and_return(swagger_format)
             subject.stop(notification)
           end
 
           let(:notification) { double('notification') }
 
-          it 'writes the swagger_doc(s) to file' do
-            expect(File).to exist("#{swagger_root}/v1/swagger.json")
-            expect(File).to exist("#{swagger_root}/v2/swagger.json")
+          context 'with default format' do
+            let(:swagger_format) { :json }
+
+            it 'writes the swagger_doc(s) to file' do
+              expect(File).to exist("#{swagger_root}/v1/swagger.json")
+              expect(File).to exist("#{swagger_root}/v2/swagger.json")
+              expect { JSON.parse(File.read("#{swagger_root}/v2/swagger.json")) }.not_to raise_error
+            end
+          end
+
+          context 'with yaml format' do
+            let(:swagger_format) { :yaml }
+
+            it 'writes the swagger_doc(s) as yaml' do
+              expect(File).to exist("#{swagger_root}/v1/swagger.json")
+              expect { JSON.parse(File.read("#{swagger_root}/v1/swagger.json")) }.to raise_error(JSON::ParserError)
+              # Psych::DisallowedClass would be raised if we do not pre-process ruby symbols
+              expect { YAML.safe_load(File.read("#{swagger_root}/v1/swagger.json")) }.not_to raise_error
+            end
           end
 
           after do