With Rspec you can mock objects or functions, for example like this:
expect(my_object).to receive(:my_function).and_return('hello world')
Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)
It's also easy to remove mocks for an object:
RSpec::Mocks.space.proxy_for(my_object).reset