Rack [already implements `redirect?` on the response object](https://github.com/rack/rack/blob/1569a985e17d9caaf94d0e97d95ef642c4ab14ba/lib/rack/response.rb#L141) so we don't need to implement our own.
We shouldn't depend on specific methods imlemented in the TestResponse subclass because the response could actually be a real response object. In the future, we should either push the aliased predicate methods in TestResponse up to the real response object, or remove them
This will save Travis some precious resource since it will not need to run 18 jobs for these Ruby implementations on every push or pull request. We do care about these implementations but we should fix the build locally before having it running on travis. We would love to have someone working on this but right now it is not our reality.
The concurrent-ruby gem is a toolset containing many concurrency utilities. Many of these utilities include runtime-specific optimizations when possible. Rather than clutter the Rails codebase with concurrency utilities separate from the core task, such tools can be superseded by similar tools in the more specialized gem. This commit replaces `ActiveSupport::Concurrency::Latch` with `Concurrent::CountDownLatch`, which is functionally equivalent.
These comments do not add a lot to the readability, grepability or overall understanding of the tests, therefore I believe they can be safely removed.