Cache Note#notable for commits and fix tests

app/models/note.rb

@@ -190,7 +190,7 @@ class Note < ActiveRecord::Base
   # override to return commits, which are not active record
   def noteable
     if for_commit?
-      project.commit(commit_id)
+      @commit ||= project.commit(commit_id)
     else
       super
     end

spec/factories/commits.rb

@@ -4,14 +4,19 @@ FactoryGirl.define do
   factory :commit do
     git_commit RepoHelpers.sample_commit
     project factory: :empty_project
-    author { build(:author) }
 
     initialize_with do
       new(git_commit, project)
     end
 
+    after(:build) do |commit|
+      allow(commit).to receive(:author).and_return build(:author)
+    end
+
     trait :without_author do
-      author nil
+      after(:build) do |commit|
+        allow(commit).to receive(:author).and_return nil
+      end
     end
   end
 end

spec/features/participants_autocomplete_spec.rb

@@ -54,7 +54,8 @@ feature 'Member autocomplete', :js do
     let(:note) { create(:note_on_commit, project: project, commit_id: project.commit.id) }
 
     before do
-      allow_any_instance_of(Commit).to receive(:author).and_return(author)
+      allow(User).to receive(:find_by_any_email)
+        .with(noteable.author_email.downcase).and_return(author)
 
       visit project_commit_path(project, noteable)
     end

spec/services/notification_service_spec.rb

@@ -383,7 +383,7 @@ describe NotificationService, services: true do
       before do
         build_team(note.project)
         reset_delivered_emails!
-        allow_any_instance_of(Commit).to receive(:author).and_return(@u_committer)
+        allow(note.noteable).to receive(:author).and_return(@u_committer)
         update_custom_notification(:new_note, @u_guest_custom, resource: project)
         update_custom_notification(:new_note, @u_custom_global)
       end