Make null_store the default cache store in test environment config

[mcnelson]

Summary

It's surprising to me that by default, low-level caching is functional in the test environment. This simply adds config.cache_store = :null_store in config/environments/test.rb.

The existing defaults in test.rb as well as the Rails Guides kinda have you believe the null_store is the default.

Really was on the fence about opening this as it may not be a substantial enough change to warrant dev resources. But since Rails has such a great reputation of providing sane defaults, I felt like this would be worth it.

Other Information

I perused the tests and wasn't sure where best to add anything. railties/test/application/generators_test.rb?

Appropriate to update CHANGELOG?

[rails-bot]

Thanks for the pull request, and welcome! The Rails team is excited to review your changes, and you should hear from @eileencodes (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

This repository is being automatically checked for code quality issues using Code Climate. You can see results for this analysis in the PR status below. Newly introduced issues should be fixed before a Pull Request is considered ready to review.

Please see the contribution instructions for more information.

[georgeclaghorn]

I’ve stubbed my toe on this before. 👍

Nothing changes for existing apps unless they opt into the new default via rails app:update, so I don’t think a changelog entry is necessary. Thanks!

[eileencodes]

@mcnelson can you open a new PR with a changelog? It's important to mention this change in behavior.

[mcnelson]

Done: #33779

[Kerrick]

This default means rate_limit doesn't work in test environments by default, which was a surprising foot gun when I tried covering the Rails 8 authentication generator's files. It could be worth mentioning in the rate_limit docs that in order to test rate limiting, you'll need to change config.cache_store = :null_store to config.cache_store = :memory_store in config/environments/test.rb. It would go great in or after this paragraph:

Rate limiting relies on a backing ActiveSupport::Cache store and defaults to config.action_controller.cache_store, which itself defaults to the global config.cache_store. If you don’t want to store rate limits in the same datastore as your general caches, you can pass a custom store in the store parameter.

[zzak]

@Kerrick Would you mind sending a PR?

[callmesangio]

I recently had a hard time testing rate limits on controllers.

Ideally, I think the best would be to be able to swap caching backend on-demand. That is, rather than globally switch to config.cache_store = :memory_store in config/environments/test.rb, leave it to :null_store and then explicitly opt-in to :memory_store around a block in specific test methods.

It seems to me that AS::Cache::NullStore could potentially be used exactly like this, since it prepends AS::Cache::Strategy::LocalCache, which provides a with_local_cache method that allows enabling a temporary in-memory cache. Unfortunately, the increment method (the one used for rate limiting purposes) bypasses the local cache (I can't tell exactly why), so this is not viable for testing rate limits.

FWIW, I've come up with a custom solution:

# config/environments/test.rb
require "cache/store_proxy"

Rails.application.configure do
  # ...
  config.cache_store = StoreProxy.new
  # ...
end

# lib/cache/store_proxy.rb
class StoreProxy
  def initialize(...)
    @store = ActiveSupport::Cache::NullStore.new(...)
  end

  def self.supports_cache_versioning?
    true
  end

  def with_memory_store(...)
    was_store = @store
    @store = ActiveSupport::Cache::MemoryStore.new(...)
    yield
  ensure
    @store = was_store
  end

  def method_missing(name, ...)
    @store.send(name, ...)
  end
end

Then, in a test:

test "create is rate limited" do
  params = { email_address: "foo@example.com", password: "wrong" }

  Rails.cache.with_memory_store do
    10.times do
      post(session_path, params:)
      assert_response :redirect
    end

    post(session_path, params:)

    assert_response 429
  end
end

Nothing too hard to implement, really, but I think it would be nice if Rails would provide a more fine-grained solution for controlling caching in rate limit tests.

Let me know if you want to talk about this further.