Include Redis in Workhorse-in-test-suite integration

We started using Workhorse in feature tests, but no `config.toml` was
provided. As a result, we missed a startup issue that could have been
caught by testing the config loading.

A small subset of Workhorse functionality also relies on Workhorse and
Rails sharing a Redis database. If we configure it here, we can enhance
the runner API testing in rails to ensure it behaves as expected.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/209245

changelogs/unreleased/sh-include-redis-in-workhorse-test.yml

+---
+title: Include Redis in Workhorse-in-test-suite integration
+merge_request: 40026
+author:
+type: other

lib/gitlab/setup_helper.rb

@@ -28,6 +28,26 @@ module Gitlab
     end
     # rubocop:enable Rails/Output
 
+    module Workhorse
+      extend Gitlab::SetupHelper
+      class << self
+        def configuration_toml(dir, _)
+          config = { redis: { URL: redis_url } }
+
+          TomlRB.dump(config)
+        end
+
+        def redis_url
+          data = YAML.load_file(Rails.root.join('config/resque.yml'))
+          data.dig(Rails.env, 'url')
+        end
+
+        def get_config_path(dir)
+          File.join(dir, 'config.toml')
+        end
+      end
+    end
+
     module Gitaly
       extend Gitlab::SetupHelper
       class << self

spec/support/helpers/test_env.rb

@@ -247,8 +247,9 @@ module TestEnv
       'GitLab Workhorse',
       install_dir: workhorse_dir,
       version: Gitlab::Workhorse.version,
-      task: "gitlab:workhorse:install[#{install_workhorse_args}]"
-    )
+      task: "gitlab:workhorse:install[#{install_workhorse_args}]") do
+        Gitlab::SetupHelper::Workhorse.create_configuration(workhorse_dir, nil)
+      end
   end
 
   def workhorse_dir
@@ -259,6 +260,14 @@ module TestEnv
     host = "[#{host}]" if host.include?(':')
     listen_addr = [host, port].join(':')
 
+    config_path = Gitlab::SetupHelper::Workhorse.get_config_path(workhorse_dir)
+
+    # This should be set up in setup_workhorse, but since
+    # component_needs_update? only checks that versions are consistent,
+    # we need to ensure the config file exists. This line can be removed
+    # later after a new Workhorse version is updated.
+    Gitlab::SetupHelper::Workhorse.create_configuration(workhorse_dir, nil) unless File.exist?(config_path)
+
     workhorse_pid = spawn(
       { 'PATH' => "#{ENV['PATH']}:#{workhorse_dir}" },
       File.join(workhorse_dir, 'gitlab-workhorse'),
@@ -266,10 +275,7 @@ module TestEnv
       '-documentRoot', Rails.root.join('public').to_s,
       '-listenAddr', listen_addr,
       '-secretPath', Gitlab::Workhorse.secret_path.to_s,
-      # TODO: Needed for workhorse + redis features.
-      # https://gitlab.com/gitlab-org/gitlab/-/issues/209245
-      #
-      # '-config', '',
+      '-config', config_path,
       '-logFile', 'log/workhorse-test.log',
       '-logFormat', 'structured',
       '-developmentMode' # to serve assets and rich error messages