Improve content type mismatch error message

lib/openapi_first/router/find_response.rb

@@ -16,20 +16,24 @@ def self.call(responses, status, content_type, request_method:, path:)
           return Match.new(error: Failure.new(:response_not_found, message:), response: nil)
         end
         response = FindContent.call(contents, content_type)
-        if response.nil?
-          message = "#{content_error(content_type, request_method:,
-                                                   path:)} Content-Type should be #{contents.keys.join(' or ')}."
-          return Match.new(error: Failure.new(:response_not_found, message:), response: nil)
-        end
+        return response_not_found(content_type:, contents:, request_method:, path:) unless response
 
         Match.new(response:, error: nil)
       end
 
-      def self.content_error(content_type, request_method:, path:)
-        return 'Response Content-Type must not be empty.' if content_type.nil? || content_type.empty?
-
-        "Response Content-Type #{content_type} is not defined for #{request_method} #{path}."
+      def self.response_not_found(content_type:, contents:, request_method:, path:)
+        empty_content = content_type.nil? || content_type.empty?
+        message =
+          "Content-Type should be #{contents.keys.join(' or ')}, " \
+          "but was #{empty_content ? 'empty' : content_type} for " \
+          "#{request_method.upcase} #{path}"
+
+        Match.new(
+          error: Failure.new(:response_not_found, message:),
+          response: nil
+        )
       end
+      private_class_method :response_not_found
 
       def self.find_status(responses, status)
         # According to OAS status has to be a string,

spec/middlewares/response_validation_spec.rb

@@ -51,7 +51,7 @@
     end
 
     it 'returns an error' do
-      msg = 'Response Content-Type must not be empty. Content-Type should be application/json.'
+      msg = 'Content-Type should be application/json, but was empty for GET /pets'
       expect do
         get '/pets'
       end.to raise_error OpenapiFirst::ResponseNotFoundError, msg

spec/router/find_response_spec.rb

@@ -82,7 +82,7 @@ def find(responses, status, content_type)
           double(status: '200', content_type: 'application/text'),
           double(status: '200', content_type: 'application/xml')
         ]
-        message = 'Response Content-Type application/json is not defined for GET /stations. Content-Type should be application/text or application/xml.'
+        message = 'Content-Type should be application/text or application/xml, but was application/json for GET /stations'
         expect(find(responses, 200, 'application/json')).to have_attributes(
           response: nil,
           error: have_attributes(type: :response_not_found, message:)