ruby - RSpec 3 : How to stub methods and constants from code we have yet to build/add?

Question

我们正在从我们构建的名为 DBQuery 的 gem 中重构一个名为 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。

与此同时，我需要编写 RSpec 测试来验证 DBQuery 代码是否被正确调用，所有这些都没有 DBQuery。

我有的是:

代码—

gem 密码—

module DBQuery
  class Query
    MAX = 1000

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

应用程序代码—

  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

我不知道如何以不需要 DBQuery 的方式 stub 。我的错误是:

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

我不知道为什么 DBQuery::Query 被表示为一个模块，或者如何让它识别"new"。

Answer 1

据我了解，您想对 DBQuery::Query 做出期望，而不是在您的代码中定义它。 rspec-mocks 可以 stub an undefined constant ，就像您对 DBQuery::Query::MAX 所做的一样。要完全 stub DBQuery::Query，请创建一个 class double首先在你的测试中为它 stub 一个常量:

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

这样，您代码中的 DBQuery::Query 将返回 query_class double。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 stub 嵌套常量，例如 DBQuery::Query::MAX

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

关于样式，我更喜欢将 stub 和允许放在 let/let! 语句中，如下所示:

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

我还喜欢将返回值放在它们自己的 let 中，这样我就可以轻松更改它们。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