Rails引擎默认使用MiniTest做测试。会在test目录下创建一个测试用的最小运行环境dummy。如果使用Rspec测试，dummy路径一般放在spec/dummy。

创建一个不使用测试，dummy路径指定为spec/dummy的引擎

rails plugin new engines/my_engine --mountable --skip-test --dummy_path=spec/dummy

gemspec中添加rspec-rails

spec.add_development_dependency "rspec-rails"

引擎目录下安装gem

bundle install

安装rspec

rails g rspec:install

修改engines/my_engine/spec/rails_helper.rb

# require File.expand_path('../../config/environment', __FILE__)
require File.expand_path('dummy/config/environment', __FILE__)

测试rspec运行

rspec spec/

配置使用rspec作为测试框架，更新 /engines/my_engine/lib/my_feature/engine.rb

module MyEngine
  class Engine < ::Rails::Engine
    isolate_namespace MyFeature

    config.generators do |g|
      g.test_framework :rspec
    end
  end
end

设置migrate查找路径

把rails引擎的db/migrate和dummy/db/migrate添加进migrations_paths

begin
  ActiveRecord::Migrator.migrations_paths = [File.expand_path('dummy/db/migrate', __dir__)]
  ActiveRecord::Migration.maintain_test_schema!
rescue ActiveRecord::PendingMigrationError => e
  abort e.to_s.strip
end

添加Factory Bot

gemspec中添加 factory_bot_rails

spec.add_development_dependency "factory_bot_rails"

修改 engine.rb 文件

config.generators do |g|
  g.test_framework :rspec
  g.fixture_replacement :factory_bot
  g.factory_bot dir: 'spec/factories'
end

修改 engines/my_engine/spec/rails_helper.rb

require 'factory_bot_rails'

FactoryBot.definition_file_paths << File.join(File.dirname(__FILE__), 'factories')
FactoryBot.factories.clear
FactoryBot.find_definitions
RSpec.configure do |config|
  ...
  config.include FactoryBot::Syntax::Methods
  ...

rails g生成的factory命名空间不对，需要自己改一下

factory :car, class: MyEngine::Car

把主应用中的migration文件复制到dummy/db/migrate下

cp main_app/db/migrate/* ../engines/my_engine/spec/dummy/db/migrate/

执行数据库迁移

rails db:migrate

参考