rspec-parameterized使っていてletされた変数へのアクセスで不思議な挙動があったので、その挙動を再現したコード

failure_rspec_parameterized_spec.rb

require 'bundler/inline'
gemfile do
  source 'https://rubygems.org'
  gem 'rspec'
  gem 'rspec-parameterized'
end

require 'rspec'
require 'rspec-parameterized'

# super: no superclass method `foo' for #<RSpec::ExampleGroups::FailureCase::Context1::Context2 (no description provided)>
describe "Failure case" do
  let(:foo) { 'foo' }

  context 'context1' do
    let(:bar) { 'bar' }

    context 'context2' do
      where(:expected_string) do
        [
          [foo], # ここは ref(:foo) を使わないといけない
        ]
      end

      with_them do
        it "return foo" do
          expect(foo).to eq expected_string
        end
      end
    end
  end
end

success_rspec_parameterized_spec.rb

require 'bundler/inline'
gemfile do
  source 'https://rubygems.org'
  gem 'rspec'
  gem 'rspec-parameterized'
end

require 'rspec'
require 'rspec-parameterized'

describe "Success case" do
  let(:foo) { 'foo' }

  context 'context1' do
    context 'context2' do
      let(:bar) { 'bar' }

      where(:expected_string) do
        [
          [foo], # ここは ref(:foo) を使わないといけないはずだが、これでも動く
        ]
      end

      with_them do
        it "return foo" do
          expect(foo).to eq expected_string
        end
      end
    end
  end
end