[Ruby 3.0] improve specs for Slack action

[ainame]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

As per the plan #17931 for Ruby 3.0, I've been working on fixing Ruby 2.7's deprecation warnings which will crash on Ruby 3.0. There is an issue where one of the fastlane's dependencies slack-notifier, which is not maintained any more, keeps producing that warning.

There would be some options in solving that issue -

1. Ping the maintainers and ask them to release a new version
2. Fork the repo and publish it as a different gem, like fastlane-slack-notifier
3. Replace the gem with our own one

In my opinion, 1 is too little hope and 2 would be too much. I would go with 3 as I've got this rewritten one tailored for fastlane's use-case within 60 LoC, which I think is fair to have its own implementation. #18537

So, in order to migrate the Slack action, I'd like to prepare for it by improving the testability of it. Prior to this PR, slack_spec.rb uses a hack that makes it return specific objects to verify instead of performing its process entirely. That pulls out Slack::Notifier object from the gem to unit tests. Meaning the unit tests will be completely broken when removing the dependency. This PR makes the test cases independent from the gem.

Description

There are two parts to this PR. The first one is to extract logic in Fastlane::SlackAction.run into a runner class that allows me to mock a network request to Slack by expect(..).to receive(...).with(...) in rspec-mocks. It is a simpler approach than using the Helper.test? hack. The second one is to use argument matcher to describe what parameters are given to the method handling network requests without having to depend on slack-notifier gem.

-        notifier, attachments = Fastlane::Actions::SlackAction.run(options)
-
-        expect(notifier.config.defaults[:username]).to eq('fastlane')
-        expect(notifier.config.defaults[:channel]).to eq(channel)
-
-        expect(attachments[:color]).to eq('danger')
-        expect(attachments[:text]).to eq(message)
-        expect(attachments[:pretext]).to eq(nil)
-
-        fields = attachments[:fields]
-        expect(fields[1][:title]).to eq('Built by')
-        expect(fields[1][:value]).to eq('Jenkins')
-
-        expect(fields[2][:title]).to eq('Lane')
-        expect(fields[2][:value]).to eq(lane_name)
-
-        expect(fields[3][:title]).to eq('Result')
-        expect(fields[3][:value]).to eq('Error')
+        expected_args = {
+          attachments: [
+            hash_including(
+              color: 'danger',
+              pretext: nil,
+              text: message,
+              fields: array_including(
+                { title: 'Built by', value: 'Jenkins', short: false },
+                { title: 'Lane', value: lane_name, short: true },
+                { title: 'Result', value: 'Error', short: true },
+              )
+            )
+          ],
+          link_names: false,
+          icon_url: 'https://fastlane.tools/assets/img/fastlane_icon.png',
+          fail_on_error: true,
+        }
+        expect(subject).to receive(:post_message).with(expected_args)
+        subject.run(options)

Argument Matcher is much more descriptive than using many assertions to verify a big Hash object🙁

Testing Steps

Add a lane like below to fastlane/Fastfile in this repo's clone.

lane :slack_test do
  slack(
    slack_url: 'https://hooks.slack.com/services/xxxxxxxxxxx',
    pretext: 'pretext test <@xxxxxx> #general',
    username: 'ainame-bot',
    channel: '#general',
    message: 'test <@xxxxxx> #general',
    link_names: true,
  )
end

[ainame]

I've got feedback to keep this method working here.
#18537 (comment)

[rogerluan]

Just a UX comment, other than that this PR LGTM 💪

[rogerluan]

Since we don't support Block Kit yet (do we?), I'm concerned to be marking something as deprecated without offering an alternative to users yet 🤔

[ainame]

What do you think about this?
#18512 (comment)

I guess UI.deprecated is not necessarily meant to provide alternatives and can be used to announce future removal 🤔 I mean most users won't see this message. Only plugin users whose plugins refer to this method directly, like this plugin, will see it.

https://github.com/crazymanish/fastlane-plugin-slack_bot/blob/0ca42f4d8f6f6d7cdd02f54615210a6ae254eed9/lib/fastlane/plugin/slack_bot/actions/update_slack_message.rb#L16

[joshdholtz]

This is such a high quality code change! I’m learning so much about better code architecture from you 😍

[fastlane-bot]

Congratulations! 🎉 This was released as part of fastlane 2.181.0 🚀