RSpec自定义匹配器保持规范之间的状态

Question

我在RSpec（2.8.0）自定义匹配器功能中遇到了一些违反直觉的行为，我想知道这是一个bug或功能，还是我感到困惑。让我们看看代码：

# matcher code
RSpec::Matchers.define :exist do
  chain :with_start_time do |time|
    @start_time = time
  end
  chain :with_end_time do |time|
    @end_time = time
  end
  match do |subject|
    result = true
    result &&= subject.start_time == @start_time if @start_time
    result &&= subject.end_time == @end_time if @end_time
    result
  end
  failure_message_for_should do |subject|
    "Failure!n".tap do |msg|
      if @start_time != subject.start_time
        msg << "Expected start_time to be #@start_time but was #{subject.start_time}n"
      end
      if @end_time != subject.end_time
        msg << "Expected end_time to be #@end_time but was #{subject.end_time}n"
      end
    end
  end
end
#spec code
require 'ostruct'
describe 'RSpec custom matcher keeping state between tests' do
  let(:time) { Time.now }
  it 'passes the first spec' do
    o = OpenStruct.new(start_time: time)
    o.should exist.with_start_time(time)
  end
  it 'fails the second because matcher kept @start_time from the first test' do
    o = OpenStruct.new(end_time: time)
    o.should exist.with_end_time(time)
  end
end

失败（证明问题）：

avetia01:~/projects/custom_matcher_bug% rspec test_spec.rb             
.F
Failures:
  1) RSpec custom matcher keeping state between tests fails the second because matcher kept @start_time from the first test
     Failure/Error: o.should exist.with_end_time(time)
       Failure!
       Expected start_time to be 2012-02-27 12:20:25 +0000 but was 
     # ./test_spec.rb:41:in `block (2 levels) in <top (required)>'
Finished in 0.00116 seconds
2 examples, 1 failure

因此，出乎意料的是，同一个matcher实例似乎在多个规范中使用。在这种特殊情况下，这导致@start_time被第一个规范的值初始化，导致第二个规范的错误失败。

Answer 1

这已经报告并修复，但尚未发布：

https://github.com/rspec/rspec-expectations/issues/104