puffing-billy | A rewriting web proxy for testing interactions between your browser and external sites. Works with | Proxy library

This is most likely because you're using a very old version of capybara-webkit. If you don't need the latest Capybara lock the version of capybara-webkit in your Gemfile to ~>1.14 (latest release) If you do need the latest Capybara you'll have to tell your Gemfile to use the master branch of capybara-webkit.

The errors are many here, so let's just start at the beginning

1. You don't have require capybara/rails in your spec_helper.rb or rails_helper.rb - https://github.com/teamcapybara/capybara#setup - this means Capybara.app isn't getting set and is why you're getting the "rack-test requires a rack application" - of course you don't really want to be using the rack-test driver for your current test which #3 will deal with.

2. Capybara already includes Capybara::DSL into feature specs, so use feature specs, and remove the include Capybara::DSL from your RSpec config shown above. This requires either putting your spec file into spec/features/my_spec.rb and enabling the RSpec config to determine test type by directory, or manually specifying that the test is a feature spec

I'm assuming you mean Rails 5.1 since Rails 5 doesn't have system tests.

1. The copy of the application Capybara runs for testing is run in a separate thread, not a separate process. This means they do have access to the same memory, and loaded classes

2. There is nothing special required for configuring WebMock or VCR beyond what their READMEs already provide

3. The setup of Capybara and how Rails handles it is irrelevant to the configuration of WebMock or VCR. Additionally, even when using Rails 5.1 system tests all of the normal Capybara configuration options are still usable.

That all being said, there are a couple of things to be aware of here. Firstly, WebMock/VCR can only deal with requests made by your app (not from the browser which you stated you don't need) and it's generally better to use faked services (if possible) rather than WebMock/VCR when doing end to end system tests since there is less interference with the code under test.

If this doesn't answer your issues, post a question with a specific issue you're having, the code that's causing your issue, and the error you're getting.