RSpec 3:如何从我们尚未构建/添加的代码中存根方法和常量？

Question

我们正在从我们构建的名为DBQuery的gem重构一个名为DataSourceIntegrations的Ruby应用程序.我正在将一些DBQuery代码迁移到DataSourceIntegrations中.我正在构建的部分取决于DBQuery,它将在单独的步骤中添加.

同时,我需要编写RSpec测试来验证是否正确调用了DBQuery代码,所有这些都没有DBQuery.

我有的是:

码-

宝石代码 -

module DBQuery
  class Query
    MAX = 1000

    def retrieve_users
      # Returns an array of user IDs
    end
  end
end

申请代码 -

  module Integration
    def initialize
      @query = DBQuery::Query.new
    end   
  end

  module Integration
    class StackOverflowIntegration
      include Integration

      def query
        users = []
        while (users < DBQuery::Query::MAX) do
          # Creates a users buffer
          users.push @query.retrieve_users(users_buffer)
        end
      end
    end   
  end

测试─

describe Integration::StackOverflowIntegration do
  let(:db_query) { double('DBQuery::Query') }

  before do
    stub_const('DBQuery::Query::MAX', 1000)
    allow(db_query).to receive(:new).and_return(db_query)
    allow(db_query).to receive(:retrieve_users).and_return([1000, 1001, 1002])
  end

  it 'queries without error' do
    expect { StackOverflowIntegration.new.query }.to_not raise_error
  end
end

我无法弄清楚如何以不需要DBQuery的方式存根.我的错误是:

NoMethodError:
       undefined method `new' for #<Module:0x007fa7ce561968>

我不知道为什么DBQuery :: Query被表示为模块,或者如何让它识别"new".

Answer 1

据我了解,您希望在DBQuery::Query不在代码中定义它的情况下提出期望.rspec-mocks可以存储未定义的常量,就像你所做的那样DBQuery::Query::MAX.要DBQuery::Query完全存根,首先创建一个类double,并在测试中为它存根一个const:

db_query__query_class = class_double('DBQuery::Query')
stub_const('DBQuery::Query', db_query__query_class)

这样,DBQuery::Query在你的代码中将返回query_classdouble.然后你可以用它定义一些行为:

query_instance = instance_double('DBQuery::Query')
allow(db_query__query_class).to receive(:new).and_return(query_instance)
allow(db_query).to receive(:retrieve_users).and_return([1000, 1001, 1002])

您仍然需要存根嵌套常量 DBQuery::Query::MAX

stub_const('DBQuery::Query::MAX', 1000)

关于样式,我更喜欢放置存根并允许在let/ let!语句中这样:

describe Integration::StackOverflowIntegration do
  let!(:db_query__query_class) do
    class_double('DBQuery::Query').tap do |double|
      stub_const('DBQuery::Query', double)
      stub_const('DBQuery::Query::MAX', 1000)
      allow(double).to receive(:new).and_return(query_instance)
    end
  end
  let(:query_instance) do
    instance_double('DBQuery::Query').tap do |double|
      allow(double).to receive(:retrieve_users).and_return([1000, 10001, 1002])
    end
  end
end

另外,我喜欢将返回的值放在自己的位置,let以便我可以轻松更改它们.这是一个完整的工作(和虚拟)示例:

RSpec.configure do |c|
  c.around(:context, :protect_with_timeout) do |example|
    Timeout::timeout(2) {
      example.run
    }
  end
end

describe Integration::StackOverflowIntegration do
  let!(:db_query__query_class) do
    class_double('DBQuery::Query').tap do |double|
      stub_const('DBQuery::Query', double)
      stub_const('DBQuery::Query::MAX', max_queries)
      allow(double).to receive(:new).and_return(query_instance)
    end
  end
  let(:query_instance) do
    instance_double('DBQuery::Query').tap do |double|
      allow(double).to receive(:retrieve_users).and_return(retrieved_users)
    end
  end
  let(:max_queries) { 1000 }
  let(:retrieved_users) { [1000, 1001, 1002] }

  describe '#query' do
    subject(:stack_overflow_query) { Integration::StackOverflowIntegration.new.query }

    it 'queries without error in nominal case' do
      expect { stack_overflow_query }.to_not raise_error
    end

    context 'with 0 users returned' do
      let(:retrieved_users) { [] }

      it 'does not loop forever', :protect_with_timeout do
        pending('not implemented yet...')
        stack_overflow_query # will timeout
      end
    end

    context 'with 10 users returned' do
      let(:retrieved_users) { [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] }

      it 'calls #retrieve_users 100 times' do
        stack_overflow_query
        expect(query_instance).to have_received(:retrieve_users).exactly(100).times
      end
    end

    context 'with DBQuery::Query::MAX set to 0' do
      let(:max_queries) { 0 }

      it 'does not call #retrieve_users at all' do
        stack_overflow_query
        expect(query_instance).not_to have_received(:retrieve_users)
      end
    end
  end
end