Introduce Turbo::SystemTestHelper

Introduce the `Turbo::SystemTestHelper` module to be included into
[ActionDispatch::SystemTestCase][] when it's available.

The module is named to mimic [ActionText::SystemTestHelper][].

The module defines a `#connect_turbo_cable_stream_sources` helper
method extracted from this project's System Test suite. It aims to
synchronize the test harness with Turbo's Action Cable-powered broadcast
support. The method will find all `<turbo-cable-stream-source>` elements
that are present but not yet `[connected]` (returning the results
immediately with Capybara's `:wait`), then wait for them to connect
(using whatever Capybara's configured wait value).

In addition to the `connect_turbo_cable_stream_sources`, also introduce
a `:turbo_cable_stream_source` Capybara selector, along with
`assert_turbo_cable_stream_source` and
`assert_no_turbo_cable_stream_source` helper methods.

[ActionDispatch::SystemTestCase]: https://edgeapi.rubyonrails.org/classes/ActionDispatch/SystemTestCase.html
[ActionText::SystemTestHelper]: https://edgeapi.rubyonrails.org/classes/ActionText/SystemTestHelper.html

README.md

@@ -56,15 +56,15 @@ When the user clicks on the `Edit this todo` link, as a direct response to this
 
 ### A note on custom layouts
 
-In order to render turbo frame requests without the application layout, Turbo registers a custom [layout method](https://api.rubyonrails.org/classes/ActionView/Layouts/ClassMethods.html#method-i-layout). 
+In order to render turbo frame requests without the application layout, Turbo registers a custom [layout method](https://api.rubyonrails.org/classes/ActionView/Layouts/ClassMethods.html#method-i-layout).
 If your application uses custom layout resolution, you have to make sure to return `"turbo_rails/frame"` (or `false` for TurboRails < 1.4.0) for turbo frame requests:
 
 ```ruby
 layout :custom_layout
 
 def custom_layout
   return "turbo_rails/frame" if turbo_frame_request?
-  
+
   # ... your custom layout logic
 ```
 
@@ -81,7 +81,7 @@ layout :custom_layout
 
 def custom_layout
   return "turbo_rails/frame" if turbo_frame_request?
-  
+
   "some_static_layout"
 ```
 
@@ -100,6 +100,64 @@ This gem provides a `turbo_stream_from` helper to create a turbo stream.
 <%# Rest of show here %>
 ```
 
+### Testing Turbo Stream Broadcasts
+
+Receiving server-generated Turbo Broadcasts requires a connected Web Socket.
+Views that render `<turbo-cable-stream-source>` elements with the
+`#turbo_stream_from` view helper incur a slight delay before they're ready to
+receive broadcasts. In System Tests, that delay can disrupt Capybara's built-in
+synchronization mechanisms that wait for or assert on content that's broadcast
+over Web Sockets. For example, consider a test that navigates to a page and then
+immediately asserts that broadcast content is present:
+
+```ruby
+test "renders broadcasted Messages" do
+  message = Message.new content: "Hello, from Action Cable"
+
+  visit "/"
+  click_link "All Messages"
+  message.save! # execute server-side code to broadcast a Message
+
+  assert_text message.content
+end
+```
+
+If the call to `Message#save!` executes quickly enough, it might beat-out any
+`<turbo-cable-stream-source>` elements rendered by the call to `click_link "All
+Messages"`.
+
+To wait for any disconnected `<turbo-cable-stream-source>` elements to connect,
+call [`#connect_turbo_cable_stream_sources`](turbo-rails/blob/wait-for-cable-stream-sourceshttps://github.com/hotwired/turbo-rails/blob/main/lib/turbo/system_test_helper.rb):
+
+```diff
+ test "renders broadcasted Messages" do
+   message = Message.new content: "Hello, from Action Cable"
+
+   visit "/"
+   click_link "All Messages"
++  connect_turbo_cable_stream_sources
+   message.save! # execute server-side code to broadcast a Message
+
+   assert_text message.content
+ end
+```
+
+By default, calls to [`#visit`](https://rubydoc.info/github/teamcapybara/capybara/master/Capybara/Session:visit) will wait for all `<turbo-cable-stream-source>` elements to connect. You can control this by modifying the `config.turbo.test_connect_after_actions`. For example, to wait after calls to [`#click_link`](https://rubydoc.info/github/teamcapybara/capybara/master/Capybara/Node/Actions:click_link), add the following to `config/environments/test.rb`:
+
+```ruby
+# config/environments/test.rb
+
+config.turbo.test_connect_after_actions << :click_link
+```
+
+To disable automatic connecting, set the configuration to `[]`:
+
+```ruby
+# config/environments/test.rb
+
+config.turbo.test_connect_after_actions = []
+```
+
 [See documentation](https://turbo.hotwired.dev/handbook/streams).
 
 ## Installation
@@ -139,6 +197,7 @@ Note that this documentation is updated automatically from the main branch, so i
 - [Turbo Test Assertions](https://rubydoc.info/github/hotwired/turbo-rails/main/Turbo/TestAssertions)
 - [Turbo Integration Test Assertions](https://rubydoc.info/github/hotwired/turbo-rails/main/Turbo/TestAssertions/IntegrationTestAssertions)
 - [Turbo Broadcastable Test Helper](https://rubydoc.info/github/hotwired/turbo-rails/main/Turbo/Broadcastable/TestHelper)
+- [Turbo System Test Helper](https://rubydoc.info/github/hotwired/turbo-rails/main/Turbo/SystemTestHelper)
 
 ## Compatibility with Rails UJS
 

lib/turbo/engine.rb

@@ -5,6 +5,7 @@ class Engine < Rails::Engine
     isolate_namespace Turbo
     config.eager_load_namespaces << Turbo
     config.turbo = ActiveSupport::OrderedOptions.new
+    config.turbo.test_connect_after_actions = %i[visit]
     config.autoload_once_paths = %W(
       #{root}/app/channels
       #{root}/app/controllers
@@ -111,5 +112,24 @@ class TurboStreamEncoder < IdentityEncoder
         end
       end
     end
+
+    initializer "turbo.system_test_helper" do
+      ActiveSupport.on_load(:action_dispatch_system_test_case) do
+        require "turbo/system_test_helper"
+        include Turbo::SystemTestHelper
+      end
+    end
+
+    config.after_initialize do |app|
+      ActiveSupport.on_load(:action_dispatch_system_test_case) do
+        app.config.turbo.test_connect_after_actions.map do |method|
+          class_eval <<~RUBY, __FILE__, __LINE__ + 1
+            def #{method}(...)                                    # def visit(...)
+              super.tap { connect_turbo_cable_stream_sources }   #   super.tap { connect_turbo_cable_stream_sources }
+            end                                                   # end
+          RUBY
+        end
+      end
+    end
   end
 end

lib/turbo/system_test_helper.rb

@@ -0,0 +1,128 @@
+module Turbo::SystemTestHelper
+  # Delay until every `<turbo-cable-stream-source>` element present in the page
+  # is ready to receive broadcasts
+  #
+  #   test "renders broadcasted Messages" do
+  #     message = Message.new content: "Hello, from Action Cable"
+  #
+  #     visit "/"
+  #     click_link "All Messages"
+  #     message.save! # execute server-side code to broadcast a Message
+  #
+  #     assert_text message.content
+  #   end
+  #
+  # By default, calls to `#visit` will wait for all `<turbo-cable-stream-source>`
+  # elements to connect. You can control this by modifying the
+  # `config.turbo.test_connect_after_actions`. For example, to wait after calls to
+  # `#click_link`, add the following to `config/environments/test.rb`:
+  #
+  #   # config/environments/test.rb
+  #   config.turbo.test_connect_after_actions << :click_link
+  #
+  # To disable automatic connecting, set the configuration to `[]`:
+  #
+  #   # config/environments/test.rb
+  #   config.turbo.test_connect_after_actions = []
+  #
+  def connect_turbo_cable_stream_sources(**options, &block)
+    all(:turbo_cable_stream_source, **options, connected: false, wait: 0).each do |element|
+      element.assert_matches_selector(:turbo_cable_stream_source, **options, connected: true, &block)
+    end
+  end
+
+  # Asserts that a `<turbo-cable-stream-source>` element is present in the
+  # document
+  #
+  # ==== Arguments
+  #
+  # * <tt>locator</tt> optional locator to determine the element's
+  #   `[signed-stream-name]` attribute. Can be of any type that is a valid
+  #   argument to <tt>Turbo::Streams::StreamName#signed_stream_name</tt>.
+  #
+  # ==== Options
+  #
+  # * <tt>:connected</tt> matches the `[connected]` attribute
+  # * <tt>:channel</tt> matches the `[channel]` attribute. Can be a Class,
+  #   String, Symbol, or Regexp
+  # * <tt>:signed_stream_name</tt> matches the element's `[signed-stream-name]`
+  #   attribute. Can be of any type that is a valid
+  #   argument to <tt>Turbo::Streams::StreamName#signed_stream_name</tt>.
+  #
+  # In addition to the filters listed above, accepts any valid Capybara global
+  # filter option.
+  def assert_turbo_cable_stream_source(...)
+    assert_selector(:turbo_cable_stream_source, ...)
+  end
+
+  # Asserts that a `<turbo-cable-stream-source>` element is absent from the
+  # document
+  #
+  # ==== Arguments
+  #
+  # * <tt>locator</tt> optional locator to determine the element's
+  #   `[signed-stream-name]` attribute. Can be of any type that is a valid
+  #   argument to <tt>Turbo::Streams::StreamName#signed_stream_name</tt>.
+  #
+  # ==== Options
+  #
+  # * <tt>:connected</tt> matches the `[connected]` attribute
+  # * <tt>:channel</tt> matches the `[channel]` attribute. Can be a Class,
+  #   String, Symbol, or Regexp
+  # * <tt>:signed_stream_name</tt> matches the element's `[signed-stream-name]`
+  #   attribute. Can be of any type that is a valid
+  #   argument to <tt>Turbo::Streams::StreamName#signed_stream_name</tt>.
+  #
+  # In addition to the filters listed above, accepts any valid Capybara global
+  # filter option.
+  def assert_no_turbo_cable_stream_source(...)
+    assert_no_selector(:turbo_cable_stream_source, ...)
+  end
+
+  Capybara.add_selector :turbo_cable_stream_source do
+    xpath do |locator|
+      xpath = XPath.descendant.where(XPath.local_name == "turbo-cable-stream-source")
+      xpath.where(SignedStreamNameConditions.new(locator).reduce(:|))
+    end
+
+    expression_filter :connected do |xpath, value|
+      builder(xpath).add_attribute_conditions(connected: value)
+    end
+
+    expression_filter :channel do |xpath, value|
+      builder(xpath).add_attribute_conditions(channel: value.try(:name) || value)
+    end
+
+    expression_filter :signed_stream_name do |xpath, value|
+      case value
+      when TrueClass, FalseClass, NilClass, Regexp
+        builder(xpath).add_attribute_conditions("signed-stream-name": value)
+      else
+        xpath.where(SignedStreamNameConditions.new(value).reduce(:|))
+      end
+    end
+  end
+
+  class SignedStreamNameConditions # :nodoc:
+    include Turbo::Streams::StreamName, Enumerable
+
+    def initialize(value)
+      @value = value
+    end
+
+    def attribute
+      XPath.attr(:"signed-stream-name")
+    end
+
+    def each
+      if @value.is_a?(String)
+        yield attribute == @value
+        yield attribute == signed_stream_name(@value)
+      elsif @value.is_a?(Array) || @value.respond_to?(:to_key)
+        yield attribute == signed_stream_name(@value)
+      elsif @value.present?
+        yield attribute == @value
+      end
+    end
+  end
+end

test/dummy/app/views/messages/show.html.erb

@@ -0,0 +1,3 @@
+<h1>Message #<%= @message.id %></h1>
+
+<%= turbo_stream_from @message %>

test/system/assertions_test.rb

@@ -0,0 +1,48 @@
+require "application_system_test_case"
+
+class AssertionsTest < ApplicationSystemTestCase
+  test "#assert_turbo_cable_stream_source treats the locator as :signed_stream_name filter" do
+    message = Message.new(id: 1)
+
+    visit message_path(message)
+
+    assert_turbo_cable_stream_source message, count: 1 do |element|
+      element.assert_matches_selector :turbo_cable_stream_source, message
+      element.assert_matches_selector :turbo_cable_stream_source, [message]
+      element.assert_matches_selector :turbo_cable_stream_source, Turbo::StreamsChannel.signed_stream_name(message)
+    end
+    assert_no_turbo_cable_stream_source "junk"
+  end
+
+  test "#assert_turbo_cable_stream_source supports String collection filters" do
+    visit messages_path
+
+    assert_turbo_cable_stream_source count: 1 do |element|
+      element.assert_matches_selector :turbo_cable_stream_source
+      element.assert_matches_selector :turbo_cable_stream_source, connected: true
+      element.assert_matches_selector :turbo_cable_stream_source, channel: true
+      element.assert_matches_selector :turbo_cable_stream_source, channel: Turbo::StreamsChannel
+      element.assert_matches_selector :turbo_cable_stream_source, channel: "Turbo::StreamsChannel"
+      element.assert_matches_selector :turbo_cable_stream_source, signed_stream_name: true
+      element.assert_matches_selector :turbo_cable_stream_source, signed_stream_name: "messages"
+      element.assert_matches_selector :turbo_cable_stream_source, signed_stream_name: ["messages"]
+      element.assert_matches_selector :turbo_cable_stream_source, signed_stream_name: Turbo::StreamsChannel.signed_stream_name("messages")
+    end
+    assert_no_turbo_cable_stream_source signed_stream_name: "junk"
+    assert_no_turbo_cable_stream_source signed_stream_name: nil
+    assert_no_turbo_cable_stream_source signed_stream_name: false
+  end
+
+  test "#assert_turbo_cable_stream_source supports record filters" do
+    message = Message.new(id: 1)
+
+    visit message_path(message)
+
+    assert_turbo_cable_stream_source count: 1 do |element|
+      element.assert_matches_selector :turbo_cable_stream_source, signed_stream_name: message
+      element.assert_matches_selector :turbo_cable_stream_source, signed_stream_name: [message]
+      element.assert_matches_selector :turbo_cable_stream_source, signed_stream_name: Turbo::StreamsChannel.signed_stream_name(message)
+    end
+    assert_no_turbo_cable_stream_source signed_stream_name: [message, :junk]
+  end
+end