Add ActionCable::Channel::TestCase

ActionCable::Channel::TestCase provides an ability
to unit-test channel classes.

There are several reasons to write unit/functional cable tests:
- Access control (who has access to the channel? who can perform action and with which argument?
- Frontend-less applications have no system tests at all–and we still need a way to test channels logic.

See also #27191

2 files changed, 276 insertions, 0 deletions

diff --git a/actioncable/lib/action_cable/channel.rb b/actioncable/lib/action_cable/channel.rb
index d2f6fbbbc7..d5118b9dc9 100644
--- a/actioncable/lib/action_cable/channel.rb
+++ b/actioncable/lib/action_cable/channel.rb
@@ -11,6 +11,7 @@ module ActionCable
       autoload :Naming
       autoload :PeriodicTimers
       autoload :Streams
+      autoload :TestCase
     end
   end
 end
diff --git a/actioncable/lib/action_cable/channel/test_case.rb b/actioncable/lib/action_cable/channel/test_case.rb
new file mode 100644
index 0000000000..88d7c7092b
--- /dev/null
+++ b/actioncable/lib/action_cable/channel/test_case.rb
@@ -0,0 +1,275 @@
+# frozen_string_literal: true
+
+require "active_support"
+require "active_support/test_case"
+require "active_support/core_ext/hash/indifferent_access"
+require "json"
+
+module ActionCable
+  module Channel
+    class NonInferrableChannelError < ::StandardError
+      def initialize(name)
+        super "Unable to determine the channel to test from #{name}. " +
+          "You'll need to specify it using `tests YourChannel` in your " +
+          "test case definition."
+      end
+    end
+
+    # Stub `stream_from` to track streams for the channel.
+    # Add public aliases for `subscription_confirmation_sent?` and
+    # `subscription_rejected?`.
+    module ChannelStub
+      def confirmed?
+        subscription_confirmation_sent?
+      end
+
+      def rejected?
+        subscription_rejected?
+      end
+
+      def stream_from(broadcasting, *)
+        streams << broadcasting
+      end
+
+      def stop_all_streams
+        @_streams = []
+      end
+
+      def streams
+        @_streams ||= []
+      end
+
+      # Make periodic timers no-op
+      def start_periodic_timers; end
+      alias stop_periodic_timers start_periodic_timers
+    end
+
+    class ConnectionStub
+      attr_reader :transmissions, :identifiers, :subscriptions, :logger
+
+      def initialize(identifiers = {})
+        @transmissions = []
+
+        identifiers.each do |identifier, val|
+          define_singleton_method(identifier) { val }
+        end
+
+        @subscriptions = ActionCable::Connection::Subscriptions.new(self)
+        @identifiers = identifiers.keys
+        @logger = ActiveSupport::TaggedLogging.new ActiveSupport::Logger.new(StringIO.new)
+      end
+
+      def transmit(cable_message)
+        transmissions << cable_message.with_indifferent_access
+      end
+    end
+
+    # Superclass for Action Cable channel functional tests.
+    #
+    # == Basic example
+    #
+    # Functional tests are written as follows:
+    # 1. First, one uses the +subscribe+ method to simulate subscription creation.
+    # 2. Then, one asserts whether the current state is as expected. "State" can be anything:
+    #    transmitted messages, subscribed streams, etc.
+    #
+    # For example:
+    #
+    #   class ChatChannelTest < ActionCable::Channel::TestCase
+    #     def test_subscribed_with_room_number
+    #       # Simulate a subscription creation
+    #       subscribe room_number: 1
+    #
+    #       # Asserts that the subscription was successfully created
+    #       assert subscription.confirmed?
+    #
+    #       # Asserts that the channel subscribes connection to a stream
+    #       assert_equal "chat_1", streams.last
+    #     end
+    #
+    #     def test_does_not_subscribe_without_room_number
+    #       subscribe
+    #
+    #       # Asserts that the subscription was rejected
+    #       assert subscription.rejected?
+    #     end
+    #   end
+    #
+    # You can also perform actions:
+    #   def test_perform_speak
+    #     subscribe room_number: 1
+    #
+    #     perform :speak, message: "Hello, Rails!"
+    #
+    #     assert_equal "Hello, Rails!", transmissions.last["text"]
+    #   end
+    #
+    # == Special methods
+    #
+    # ActionCable::Channel::TestCase will also automatically provide the following instance
+    # methods for use in the tests:
+    #
+    # <b>connection</b>::
+    #      An ActionCable::Channel::ConnectionStub, representing the current HTTP connection.
+    # <b>subscription</b>::
+    #      An instance of the current channel, created when you call `subscribe`.
+    # <b>transmissions</b>::
+    #      A list of all messages that have been transmitted into the channel.
+    # <b>streams</b>::
+    #      A list of all created streams subscriptions (as identifiers) for the subscription.
+    #
+    #
+    # == Channel is automatically inferred
+    #
+    # ActionCable::Channel::TestCase will automatically infer the channel under test
+    # from the test class name. If the channel cannot be inferred from the test
+    # class name, you can explicitly set it with +tests+.
+    #
+    #   class SpecialEdgeCaseChannelTest < ActionCable::Channel::TestCase
+    #     tests SpecialChannel
+    #   end
+    #
+    # == Specifying connection identifiers
+    #
+    # You need to set up your connection manually to privide values for the identifiers.
+    # To do this just use:
+    #
+    #   stub_connection(user: users[:john])
+    #
+    # == Testing broadcasting
+    #
+    # ActionCable::Channel::TestCase enhances ActionCable::TestHelper assertions (e.g.
+    # +assert_broadcasts+) to handle broadcasting to models:
+    #
+    #
+    #  # in your channel
+    #  def speak(data)
+    #    broadcast_to room, text: data["message"]
+    #  end
+    #
+    #  def test_speak
+    #    subscribe room_id: rooms[:chat].id
+    #
+    #    assert_broadcasts_on(rooms[:chat], text: "Hello, Rails!") do
+    #      perform :speak, message: "Hello, Rails!"
+    #    end
+    #  end
+    class TestCase < ActiveSupport::TestCase
+      module Behavior
+        extend ActiveSupport::Concern
+
+        include ActiveSupport::Testing::ConstantLookup
+        include ActionCable::TestHelper
+
+        CHANNEL_IDENTIFIER = "test_stub"
+
+        included do
+          class_attribute :_channel_class
+
+          attr_reader :connection, :subscription
+          delegate :streams, to: :subscription
+
+          ActiveSupport.run_load_hooks(:action_cable_channel_test_case, self)
+        end
+
+        module ClassMethods
+          def tests(channel)
+            case channel
+            when String, Symbol
+              self._channel_class = channel.to_s.camelize.constantize
+            when Module
+              self._channel_class = channel
+            else
+              raise NonInferrableChannelError.new(channel)
+            end
+          end
+
+          def channel_class
+            if channel = self._channel_class
+              channel
+            else
+              tests determine_default_channel(name)
+            end
+          end
+
+          def determine_default_channel(name)
+            channel = determine_constant_from_test_name(name) do |constant|
+              Class === constant && constant < ActionCable::Channel::Base
+            end
+            raise NonInferrableChannelError.new(name) if channel.nil?
+            channel
+          end
+        end
+
+        # Setup test connection with the specified identifiers:
+        #
+        #   class ApplicationCable < ActionCable::Connection::Base
+        #     identified_by :user, :token
+        #   end
+        #
+        #   stub_connection(user: users[:john], token: 'my-secret-token')
+        def stub_connection(identifiers = {})
+          @connection = ConnectionStub.new(identifiers)
+        end
+
+        # Subsribe to the channel under test. Optionally pass subscription parameters as a Hash.
+        def subscribe(params = {})
+          @connection ||= stub_connection
+          # NOTE: Rails < 5.0.1 calls subscribe_to_channel during #initialize.
+          #       We have to stub before it
+          @subscription = self.class.channel_class.allocate
+          @subscription.singleton_class.include(ChannelStub)
+          @subscription.send(:initialize, connection, CHANNEL_IDENTIFIER, params.with_indifferent_access)
+          # Call subscribe_to_channel if it's public (Rails 5.0.1+)
+          @subscription.subscribe_to_channel if ActionCable.gem_version >= Gem::Version.new("5.0.1")
+          @subscription
+        end
+
+        # Unsubscribe the subscription under test.
+        def unsubscribe
+          check_subscribed!
+          subscription.unsubscribe_from_channel
+        end
+
+        # Perform action on a channel.
+        #
+        # NOTE: Must be subscribed.
+        def perform(action, data = {})
+          check_subscribed!
+          subscription.perform_action(data.stringify_keys.merge("action" => action.to_s))
+        end
+
+        # Returns messages transmitted into channel
+        def transmissions
+          # Return only directly sent message (via #transmit)
+          connection.transmissions.map { |data| data["message"] }.compact
+        end
+
+        # Enhance TestHelper assertions to handle non-String
+        # broadcastings
+        def assert_broadcasts(stream_or_object, *args)
+          super(broadcasting_for(stream_or_object), *args)
+        end
+
+        def assert_broadcast_on(stream_or_object, *args)
+          super(broadcasting_for(stream_or_object), *args)
+        end
+
+        private
+          def check_subscribed!
+            raise "Must be subscribed!" if subscription.nil? || subscription.rejected?
+          end
+
+          def broadcasting_for(stream_or_object)
+            return stream_or_object if stream_or_object.is_a?(String)
+
+            self.class.channel_class.broadcasting_for(
+              [self.class.channel_class.channel_name, stream_or_object]
+            )
+          end
+      end
+
+      include Behavior
+    end
+  end
+end