FactoryBot使用

3849 words, 11 mins

测试驱动开发中，需要构造一些数据，FactoryBot是常用的数据构造工具，语法简洁，支持多种数据构造策略，本文介绍FactoryBot在 rails 框架配合RSpec使用。

安装

添加gem到Gemfile

group :development, :test do
  gem "factory_bot_rails"
end

添加代码到spec/support/factory_bot.rb

# spec/support/factory_bot.rb
RSpec.configure do |config|
  config.include FactoryBot::Syntax::Methods
end

激活自动加载support目录, 修改spec/rails_helper.rb

Dir[Rails.root.join('spec/support/**/*.rb')].each { |f| require f }

使用案例

假如我们有一个Article的model：

有一个字段status，类型为Integer，表示文章的状态，并且可以取的值为unpublished和published,
还有个字段published_at,类型为DateTime，表示文章的发布时间

# app/model/article.rb
class Article < ApplicationRecord
  enum status: [:unpublished, :published]
end

所以我们可以定义以下测试数据：

# spec/factories/articles.rb
FactoryBot.define do
  factory :article do
    trait :published do
      status :published
    end

    trait :unpublished do
      status :unpublished
    end

    trait :in_the_future do
      published_at { 2.days.from_now }
    end

    trait :in_the_past do
      published_at { 2.days.ago }
    end
  end
end

现在我们可以在测试用例中构建数据：

# build creates an Article object without saving
build :article, :unpublished

# build_stubbed creates an Article object and acts as an already saved Article
build_stubbed :article, :published

# create creates an Article object and saves it to the database
create :article, :published, :in_the_future
create :article, :published, :in_the_past

# create_list creates a collection of objects for a given factory
# you can also use build_list and build_stubbed_list
create_list :article, 2

可以看到构建数据的策略有:

build: 只创建对象，但不入库，会触发model的validations
build_stubbed：创建对象，不入库，也不触发任何 validations
create: 创建对象，同时入库，会触发model和数据库的validations
create_list: create的批量创建方式
build_stubbed_list：build_stubbed的批量创建方式
attributes_for: 获取构造对象的属性列表

最佳实践

使用Factory linting
填充必要的字段即可
尽量使用 build 和 build_stubbed而不是 create
不要依赖默认的数据定义来进行测试
使用固定时间而不是相对时间

Factory linting

安装database_cleaner

gem :database_cleaner, group: :test

添加代码到lib/tasks/factory_bot.rake

namespace :factory_bot do
  desc "Verify that all FactoryBot factories are valid"
  task lint: :environment do
    if Rails.env.test?
      DatabaseCleaner.cleaning do
        FactoryBot.lint
      end
    else
      system("bundle exec rake factory_bot:lint RAILS_ENV='test'")
      fail if $?.exitstatus.nonzero?
    end
  end
end

执行检查

bundle exec rake factory_bot:lint

填充必要的字段即可

比如一些状态字段，需要某些条件才能触发改变，就不应该放在数据工厂定义里

# spec/factories/articles.rb
FactoryBot.define do
  factory :article do
    title "The amazing article title"

    trait :with_publish_date do
      published_at { DateTime.now }
    end
  end
end

这里我们可以使用任意选择是否需要构造带published_at的对象

let(:article_with_publish_date) { build :article, :with_publish_date }
let(:article_without_publish_date) { build :article }

不要依赖默认的数据定义来进行测试

require 'rails_helper'

RSpec.describe Article do
  describe ".published_in_the_past" do
    before do
      create :article, title: 'unpublished article'
      create :article, :published, :in_the_past, title: 'published in the past'
      create :article, :published, :in_the_future, title: 'published in the future'
    end

    subject(:article_titles) { Article.published_in_the_past.map(&:title) }

    it { expect(article_titles).to include 'published in the past' }
    it { expect(article_titles).not_to include 'unpublished article' }
    it { expect(article_titles).not_to include 'published in the future' }
  end
end

尽量使用 build 和 build_stubbed而不是 create

因为 create 会入库，如果滥用，只会让测试用例越来越慢，所以除非必要，尽量用 build 和 build_stubbed

因为 build 会把关联数据入库，如果我们不想入库，就使用build_stubbed来构造数据

# spec/factories/articles.rb
FactoryBot.define do
  factory :article do
    name 'The amazing article'
    author
  end
end

# spec/models/article_spec.rb
require 'rails_helper'

RSpec.describe Article do
  describe ".recent" do
    let(:latest)   { build_stubbed :article, :published, title: :latest  }
    let(:promoted) { build_stubbed :article, :published, title: :promoted }
  end
end

使用固定时间而不是相对时间

2.seconds.ago,5.minutes.ago可能会导致一些问题，比如统计类逻辑，所以最好用固定时间，比如

create :article, published_at: "2015-04-04T17:30:05+0700"

或者使用工具来冻住时间，比如添加ActiveSupport::Testing::TimeHelpers到RSpec的配置中

# spec/rails_helper.rb
RSpec.configure do |config|
  config.include ActiveSupport::Testing::TimeHelpers
end

可以这样使用:

before do
  travel_to Time.current
end

after do
  travel_back
end

更多的最佳实践使用方法可以参考https://github.com/thoughtbot/factory_bot/blob/master/GETTING_STARTED.md

参考自 https://semaphoreci.com/community/tutorials/working-effectively-with-data-factories-using-factorygirl

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