Environment

• jruby 9.1.13.0 (2.3.3) 2017-09-06 8e1c115 Java HotSpot(TM) 64-Bit Server VM 25.131-b11 on 1.8.0_131-b11 +jit [darwin-x86_64]
• 16.7.0 Darwin Kernel Version 16.7.0: Thu Jun 15 17:36:27 PDT 2017; root:xnu-3789.70.16~2/RELEASE_X86_64 x86_64
• rspec

I've created a sample project https://github.com/NC-phuh/jruby_rspec_bug that fully shows this issue.

Expected Behavior

module Prepender
end

class FakeClass
  prepend Prepender

  def fake_method(arg)
    return {}
  end
end

describe FakeClass do
  context "When a test stubs the prepended class" do
    it "should not persist this stub" do
      allow_any_instance_of(FakeClass)
        .to receive(:fake_method)
        .with("random argument")
        .and_return("returned value")
    end
  end

  context "when the class is no longer stubbed" do
    it "should not be affected by other tests" do
      expect(FakeClass.new.fake_method("non-random")).to eq({})
    end
  end
end

• The above test passes in MRI Ruby.

Actual Behavior

• The allow_any_instance_of is not getting cleared in jruby causing the second test to fail

Failures:

  1) FakeClass when the class is no longer stubbed should not be affected by other tests
     Failure/Error: expect(FakeClass.new.fake_method("non-random")).to eq({})

       #<FakeClass:0x74235045> received :fake_method with unexpected arguments
         expected: ("random argument")
              got: ("non-random")
        Please stub a default value first if message might be received with other args as well.
     # ./spec/rspec_scope_spec.rb:25:in `block in (root)'

Finished in 0.06384 seconds (files took 0.46047 seconds to load)
2 examples, 1 failure

It is important to note that this tests behaves as expected without a prepend Module statement.

I've traced this bug to https://github.com/rspec/rspec-mocks/blob/master/lib/rspec/mocks/any_instance/recorder.rb#L191

The line returns false even though both objects have the same id.
return unless @klass.instance_method(method_name).owner.to_s == @klass.to_s