Include broadcastable assertions automatically in ActiveSupport::Test…

…Case (hotwired#565)

* Include broadcastable assertions automatically in ActiveSupport::TestCase

* Update README

README.md

@@ -150,7 +150,7 @@ The [`Turbo::TestAssertions`](./lib/turbo/test_assertions.rb) concern provides T
 
 The [`Turbo::TestAssertions::IntegrationTestAssertions`](./lib/turbo/test_assertions/integration_test_assertions.rb) are built on top of `Turbo::TestAssertions`, and add support for passing a `status:` keyword. They are automatically included in [`ActionDispatch::IntegrationTest`](https://edgeguides.rubyonrails.org/testing.html#integration-testing).
 
-The [`Turbo::Broadcastable::TestHelper`](./lib/turbo/broadcastable/test_helper.rb) concern provides Action Cable-aware test helpers that assert that `<turbo-stream>` elements were or were not broadcast over Action Cable. They are not automatically included. To use them in your tests, make sure to `include Turbo::Broadcastable::TestHelper`.
+The [`Turbo::Broadcastable::TestHelper`](./lib/turbo/broadcastable/test_helper.rb) concern provides Action Cable-aware test helpers that assert that `<turbo-stream>` elements were or were not broadcast over Action Cable. `Turbo::Broadcastable::TestHelper` is automatically included in [`ActiveSupport::TestCase`](https://edgeapi.rubyonrails.org/classes/ActiveSupport/TestCase.html).
 
 ## Development
 

lib/turbo/engine.rb

@@ -84,6 +84,7 @@ class Engine < Rails::Engine
         require "turbo/broadcastable/test_helper"
 
         include Turbo::TestAssertions
+        include Turbo::Broadcastable::TestHelper
       end
 
       ActiveSupport.on_load(:action_dispatch_integration_test) do