Add ActionCable::Channel::TestCase

[palkan]

Follow-up #33659.

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

From #23211 (comment):

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 previous discussion here #27191

Summary

Channels Testing

Channels 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 "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!"

  # `transmissions` stores messages sent directly to the channel (i.e. with `transmit` method)
  assert_equal "Hello, Rails!", transmissions.last["text"]
end

You can set up your connection identifiers:

class ChatChannelTest < ActionCable::Channel::TestCase
  include ActionCable::TestHelper

  def test_identifiers
    stub_connection(user: users[:john])

    subscribe room_number: 1

    assert_broadcasts_on("messages_1", text: "I'm here!", from: "John") do
      perform :speak, message: "I'm here!"
    end
  end
end

When broadcasting to an object:

class ChatChannelTest < ActionCable::Channel::TestCase
  def setup
    @room = Room.find 1

    stub_connection(user: users[:john])
    subscribe room_number: room.id
  end

  def test_broadcasting
    assert_broadcasts(@room, 1) do
      perform :speak, message: "I'm here!"
    end
  end

  # or

  def test_broadcasted_data
    assert_broadcasts_on(@room, text: "I'm here!", from: "John") do
      perform :speak, message: "I'm here!"
    end
  end
end

[jeremy]

Fantastic, @palkan. Would you add a changelog entry to match?

[jeremy]

Backticks around "tests YourChannel" to be clear that it's code to be added to the test case.

[palkan]

👍

Done

[jeremy]

Let's use more precise language for these, e.g. Crazy → NonInferrable

[palkan]

I stole this craziness from action_mailer tests 🙂

Fixed

[jeremy]

Great test coverage and demonstration of the test case.

[palkan]

Thanks!

[palkan]

Would you add a changelog entry to match?

I thought we'll add one changelog entry along with the last Action Cable testing PR (this one is not the last one) since we've skipped it in #33969.

@jeremy Do you think it's better to add multiple change log entries?

[jeremy]

Sounds good re. changelog!

[y-yagi]

Is this check still necessary?

[palkan]

Oops! No, we don't need it in Rails 6.

Will send a follow-up.

Thanks for catching!