Add schema validation against OpenAPI3 specification

Gemfile

@@ -32,6 +32,7 @@ group :development, :test do
   gem 'rdoc'
   gem 'rspec', '~> 3.9'
   gem 'rubocop', '~> 1.50', require: false
+  gem "openapi3_parser", "~> 0.10.0"
 
   unless ENV['MODEL_PARSER'] == 'grape-swagger-entity'
     gem 'grape-swagger-entity', git: 'https://github.com/ruby-grape/grape-swagger-entity'

spec/spec_helper.rb

@@ -28,6 +28,15 @@
   config.include ApiClassDefinitionCleaner
   config.raise_errors_for_deprecations!
 
+  config.define_derived_metadata(file_path: /spec\/openapi_3/) do |metadata|
+    metadata[:type] ||= :openapi3
+  end
+  config.define_derived_metadata(file_path: /spec\/swagger_v2/) do |metadata|
+    metadata[:type] ||= :swagger2
+  end
+
+  config.include OpenAPI3ResponseValidationHelper, type: :openapi3
+
   config.order = 'random'
   config.seed = 40_834
 end

spec/support/open3_response_validation_helper.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require 'openapi3_parser'
+
+# This module helps to validate the response body of endpoint tests
+# against an OpenAPI 3.0 schema.
+module OpenAPI3ResponseValidationHelper
+  include RSpec::Matchers
+
+  # Sets up an `after` hook to validate the response after each test example.
+  #
+  # @param base [Class] the class including this module
+  def self.included(base)
+    base.after(:each) do
+      next unless last_response
+      next unless last_response.ok?
+
+      validate_openapi3_response(last_response.body)
+    end
+  end
+
+  # Validates the response body against an OpenAPI 3.0 schema.
+  #
+  # @param response_body [String] the response body to be validated
+  def validate_openapi3_response(response_body)
+    document = Openapi3Parser.load(response_body)
+    return if document.valid?
+
+    aggregate_failures 'validation against an OpenAPI3' do
+      document.errors.errors.each do |error|
+        expect(document.valid?).to be(true), "#{error.message} in context #{error.context}"
+      end
+    end
+  end
+end