Rails 6.1 + triple nested sub_test_case on test-unit-rails

t.rb

# frozen_string_literal: true

require 'bundler/inline'

gemfile(true) do
  source 'https://rubygems.org'

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem 'rails', github: 'rails/rails', branch: 'main'
  gem 'test-unit-rails'
end

require 'action_controller/railtie'

class TestApp < Rails::Application
  secrets.secret_key_base = config.root = __dir__

  Rails.logger  = config.logger = Logger.new($stdout)
end

require 'test/unit/rails/test_help'

class BugTest < ActionView::TestCase
  sub_test_case 'foo' do
    sub_test_case 'bar' do
    end
  end
end