Add danger rule to favor jest over karma

danger/karma/Dangerfile

+# frozen_string_literal: true
+# rubocop:disable Style/SignalException
+
+def get_karma_files(files)
+  files.select do |file|
+    file.start_with?('ee/spec/javascripts', 'spec/javascripts')
+  end
+end
+
+new_karma_files = get_karma_files(git.added_files.to_a)
+
+unless new_karma_files.empty?
+
+  if GitlabDanger.new(helper.gitlab_helper).ci?
+    markdown(<<~MARKDOWN)
+    ## New karma spec file
+
+    New frontend specs should be
+    [written in jest](https://docs.gitlab.com/ee/development/testing_guide/frontend_testing.html#jest).
+
+    You have created the following tests, please migrate them over to jest:
+
+    * #{new_karma_files.map { |path| "`#{path}`" }.join("\n* ")}
+    MARKDOWN
+  end
+
+  fail "You have created a new karma spec file"
+
+end
+
+changed_karma_files = get_karma_files(helper.all_changed_files) - new_karma_files
+
+return if changed_karma_files.empty?
+
+warn 'You have edited karma spec files. Please consider migrating them to jest.'
+
+if GitlabDanger.new(helper.gitlab_helper).ci?
+  markdown(<<~MARKDOWN)
+    ## Edited karma files
+
+    You have edited the following karma spec files. Please consider migrating them to jest:
+
+    * #{changed_karma_files.map { |path| "`#{path}`" }.join("\n* ")}
+
+    In order to align with our Iteration value, migration can also be done as a follow-up.
+
+    For more information: [Jestodus epic](https://gitlab.com/groups/gitlab-org/-/epics/895)
+  MARKDOWN
+end

lib/gitlab_danger.rb

@@ -8,6 +8,7 @@ class GitlabDanger
     duplicate_yarn_dependencies
     prettier
     eslint
+    karma
     database
     commit_messages
   ].freeze

spec/lib/gitlab_danger_spec.rb

@@ -9,7 +9,7 @@ describe GitlabDanger do
 
   describe '.local_warning_message' do
     it 'returns an informational message with rules that can run' do
-      expect(described_class.local_warning_message).to eq('==> Only the following Danger rules can be run locally: changes_size, documentation, frozen_string, duplicate_yarn_dependencies, prettier, eslint, database, commit_messages')
+      expect(described_class.local_warning_message).to eq('==> Only the following Danger rules can be run locally: changes_size, documentation, frozen_string, duplicate_yarn_dependencies, prettier, eslint, karma, database, commit_messages')
     end
   end