Create ResourceMilestoneEvents whenever milestones are changed

Use default system note content for MilestoneNote

Also update specs and fixed one typo.

Remove milestones_of method

Fix display of synthetic milestone notes

Fix display of synthetic milestone notes with direct banzai render call

Cleanup and simplify options hash

Extract ResourceEventTools module

Move some scopes and validations to resource events module

Add changelog entry

app/models/concerns/milestone_eventable.rb

+# frozen_string_literal: true
+
+module MilestoneEventable
+  extend ActiveSupport::Concern
+
+  included do
+    has_many :resource_milestone_events
+  end
+end

app/models/concerns/resource_event_tools.rb

+# frozen_string_literal: true
+
+module ResourceEventTools
+  extend ActiveSupport::Concern
+
+  included do
+    belongs_to :user
+
+    validates :user, presence: { unless: :importing? }, on: :create
+
+    validate :exactly_one_issuable
+
+    scope :created_after, ->(time) { where('created_at > ?', time) }
+  end
+
+  def exactly_one_issuable
+    issuable_count = self.class.issuable_attrs.count { |attr| self["#{attr}_id"] }
+
+    return true if issuable_count == 1
+
+    # if none of issuable IDs is set, check explicitly if nested issuable
+    # object is set, this is used during project import
+    if issuable_count == 0 && importing?
+      issuable_count = self.class.issuable_attrs.count { |attr| self.public_send(attr) } # rubocop:disable GitlabSecurity/PublicSend
+
+      return true if issuable_count == 1
+    end
+
+    errors.add(:base, "Exactly one of #{self.class.issuable_attrs.join(', ')} is required")
+  end
+end

app/models/issue.rb

@@ -15,6 +15,7 @@ class Issue < ApplicationRecord
   include ThrottledTouch
   include LabelEventable
   include IgnorableColumns
+  include MilestoneEventable
 
   DueDateStruct                   = Struct.new(:title, :name).freeze
   NoDueDate                       = DueDateStruct.new('No Due Date', '0').freeze

app/models/merge_request.rb

@@ -18,6 +18,7 @@ class MergeRequest < ApplicationRecord
   include DeprecatedAssignee
   include ShaAttribute
   include IgnorableColumns
+  include MilestoneEventable
 
   sha_attribute :squash_commit_sha
 

app/models/milestone_note.rb

+# frozen_string_literal: true
+
+class MilestoneNote < ::Note
+  attr_accessor :resource_parent, :event, :milestone
+
+  def self.from_event(event, resource: nil, resource_parent: nil)
+    resource ||= event.resource
+
+    attrs = {
+        system: true,
+        author: event.user,
+        created_at: event.created_at,
+        noteable: resource,
+        milestone: event.milestone,
+        event: event,
+        system_note_metadata: ::SystemNoteMetadata.new(action: 'milestone'),
+        resource_parent: resource_parent
+    }
+
+    if resource_parent.is_a?(Project)
+      attrs[:project_id] = resource_parent.id
+    end
+
+    MilestoneNote.new(attrs)
+  end
+
+  def note
+    @note ||= note_text
+  end
+
+  def note_html
+    @note_html ||= Banzai::Renderer.cacheless_render_field(self, :note, { group: group, project: project })
+  end
+
+  def project
+    resource_parent if resource_parent.is_a?(Project)
+  end
+
+  def group
+    resource_parent if resource_parent.is_a?(Group)
+  end
+
+  private
+
+  def note_text(html: false)
+    format = milestone&.group_milestone? ? :name : :iid
+    milestone.nil? ? 'removed milestone' : "changed milestone to #{milestone.to_reference(project, format: format)}"
+  end
+end

app/models/resource_label_event.rb

@@ -4,20 +4,17 @@ class ResourceLabelEvent < ApplicationRecord
   include Importable
   include Gitlab::Utils::StrongMemoize
   include CacheMarkdownField
+  include ResourceEventTools
 
   cache_markdown_field :reference
 
-  belongs_to :user
   belongs_to :issue
   belongs_to :merge_request
   belongs_to :label
 
-  scope :created_after, ->(time) { where('created_at > ?', time) }
   scope :inc_relations, -> { includes(:label, :user) }
 
-  validates :user, presence: { unless: :importing? }, on: :create
   validates :label, presence: { unless: :importing? }, on: :create
-  validate :exactly_one_issuable
 
   after_save :expire_etag_cache
   after_destroy :expire_etag_cache
@@ -94,22 +91,6 @@ class ResourceLabelEvent < ApplicationRecord
     end
   end
 
-  def exactly_one_issuable
-    issuable_count = self.class.issuable_attrs.count { |attr| self["#{attr}_id"] }
-
-    return true if issuable_count == 1
-
-    # if none of issuable IDs is set, check explicitly if nested issuable
-    # object is set, this is used during project import
-    if issuable_count == 0 && importing?
-      issuable_count = self.class.issuable_attrs.count { |attr| self.public_send(attr) } # rubocop:disable GitlabSecurity/PublicSend
-
-      return true if issuable_count == 1
-    end
-
-    errors.add(:base, "Exactly one of #{self.class.issuable_attrs.join(', ')} is required")
-  end
-
   def expire_etag_cache
     issuable.expire_note_etag_cache
   end

app/models/resource_milestone_event.rb

+# frozen_string_literal: true
+
+class ResourceMilestoneEvent < ApplicationRecord
+  include Gitlab::Utils::StrongMemoize
+  include Importable
+  include ResourceEventTools
+
+  belongs_to :issue
+  belongs_to :merge_request
+  belongs_to :milestone
+
+  scope :by_issue, ->(issue) { where(issue_id: issue.id) }
+  scope :by_merge_request, ->(merge_request) { where(merge_request_id: merge_request.id) }
+
+  enum action: {
+         add: 1,
+         remove: 2
+       }
+
+  # state is used for issue and merge request states.
+  enum state: Issue.available_states.merge(MergeRequest.available_states)
+
+  def self.issuable_attrs
+    %i(issue merge_request).freeze
+  end
+
+  def resource
+    issue || merge_request
+  end
+end

app/services/issuable/clone/attributes_rewriter.rb

@@ -19,6 +19,7 @@ module Issuable
 
         copy_resource_label_events
         copy_resource_weight_events
+        copy_resource_milestone_events
       end
 
       private
@@ -65,6 +66,23 @@ module Issuable
         end
       end
 
+      def copy_resource_milestone_events
+        entity_key = new_entity.class.name.underscore.foreign_key
+
+        copy_events(ResourceMilestoneEvent.table_name, original_entity.resource_milestone_events) do |event|
+          matching_destination_milestone = matching_milestone(event.milestone.title)
+
+          if matching_destination_milestone.present?
+            event.attributes
+              .except('id', 'reference', 'reference_html')
+              .merge(entity_key => new_entity.id,
+                     'milestone_id' => matching_destination_milestone.id,
+                     'action' => ResourceMilestoneEvent.actions[event.action],
+                     'state' => ResourceMilestoneEvent.states[event.state])
+          end
+        end
+      end
+
       def copy_events(table_name, events_to_copy)
         events_to_copy.find_in_batches do |batch|
           events = batch.map do |event|

app/services/issuable/common_system_notes_service.rb

@@ -22,13 +22,17 @@ module Issuable
         end
 
         create_due_date_note if issuable.previous_changes.include?('due_date')
-        create_milestone_note if issuable.previous_changes.include?('milestone_id')
+        create_milestone_note if has_milestone_changes?
         create_labels_note(old_labels) if old_labels && issuable.labels != old_labels
       end
     end
 
     private
 
+    def has_milestone_changes?
+      issuable.previous_changes.include?('milestone_id')
+    end
+
     def handle_time_tracking_note
       if issuable.previous_changes.include?('time_estimate')
         create_time_estimate_note
@@ -95,7 +99,16 @@ module Issuable
     end
 
     def create_milestone_note
-      SystemNoteService.change_milestone(issuable, issuable.project, current_user, issuable.milestone)
+      if milestone_changes_tracking_enabled?
+        # Creates a synthetic note
+        ResourceEvents::ChangeMilestoneService.new(resource: issuable, user: current_user).execute
+      else
+        SystemNoteService.change_milestone(issuable, issuable.project, current_user, issuable.milestone)
+      end
+    end
+
+    def milestone_changes_tracking_enabled?
+      ::Feature.enabled?(:track_resource_milestone_change_events, issuable.project)
     end
 
     def create_due_date_note

app/services/resource_events/change_milestone_service.rb

+# frozen_string_literal: true
+
+module ResourceEvents
+  class ChangeMilestoneService
+    attr_reader :resource, :user, :event_created_at, :resource_args
+
+    def initialize(resource:, user:, created_at: Time.now)
+      @resource = resource
+      @user = user
+      @event_created_at = created_at
+
+      @resource_args = {
+        user_id: user.id,
+        created_at: event_created_at
+      }
+    end
+
+    def execute
+      args = build_resource_args
+
+      action = if milestone.nil?
+                 :remove
+               else
+                 :add
+               end
+
+      record = args.merge(milestone_id: milestone&.id, action: ResourceMilestoneEvent.actions[action])
+
+      create_event(record)
+    end
+
+    private
+
+    def milestone
+      resource&.milestone
+    end
+
+    def create_event(record)
+      ResourceMilestoneEvent.create(record)
+
+      resource.expire_note_etag_cache
+    end
+
+    def build_resource_args
+      key = resource.class.name.underscore.foreign_key
+
+      resource_args.merge(key => resource.id, state: ResourceMilestoneEvent.states[resource.state])
+    end
+  end
+end

app/services/resource_events/merge_into_notes_service.rb

@@ -9,6 +9,11 @@ module ResourceEvents
   class MergeIntoNotesService
     include Gitlab::Utils::StrongMemoize
 
+    SYNTHETIC_NOTE_BUILDER_SERVICES = [
+      SyntheticLabelNotesBuilderService,
+      SyntheticMilestoneNotesBuilderService
+    ].freeze
+
     attr_reader :resource, :current_user, :params
 
     def initialize(resource, current_user, params = {})
@@ -24,7 +29,9 @@ module ResourceEvents
     private
 
     def synthetic_notes
-      SyntheticLabelNotesBuilderService.new(resource, current_user, params).execute
+      SYNTHETIC_NOTE_BUILDER_SERVICES.flat_map do |service|
+        service.new(resource, current_user, params).execute
+      end
     end
   end
 end

app/services/resource_events/synthetic_milestone_notes_builder_service.rb

+# frozen_string_literal: true
+
+# We store events about resource milestone changes in a separate table,
+# but we still want to display notes about milestone changes
+# as classic system notes in UI. This service generates "synthetic" notes for
+# milestone event changes.
+
+module ResourceEvents
+  class SyntheticMilestoneNotesBuilderService < BaseSyntheticNotesBuilderService
+    private
+
+    def synthetic_notes
+      return [] unless tracking_enabled?
+
+      milestone_change_events.map do |event|
+        MilestoneNote.from_event(event, resource: resource, resource_parent: resource_parent)
+      end
+    end
+
+    def milestone_change_events
+      return [] unless resource.respond_to?(:resource_milestone_events)
+
+      events = resource.resource_milestone_events.includes(user: :status) # rubocop: disable CodeReuse/ActiveRecord
+      since_fetch_at(events)
+    end
+
+    def tracking_enabled?
+      ::Feature.enabled?(:track_resource_milestone_change_events, resource.project)
+    end
+  end
+end

changelogs/unreleased/38096-splitmr-write-resource-milestone-events-pd.yml

+---
+title: Add possibility to track milestone changes on issues and merge requests
+merge_request: 24780
+author:
+type: added

ee/spec/features/issues/form_spec.rb

@@ -34,7 +34,7 @@ describe 'New/edit issue', :js do
       before do
         # Using `allow_any_instance_of`/`and_wrap_original`, `original` would
         # somehow refer to the very block we defined to _wrap_ that method, instead of
-        # the original method, resulting in infinite recurison when called.
+        # the original method, resulting in infinite recursion when called.
         # This is likely a bug with helper modules included into dynamically generated view classes.
         # To work around this, we have to hold on to and call to the original implementation manually.
         original_issue_dropdown_options = FormHelper.instance_method(:assignees_dropdown_options)

spec/controllers/projects/milestones_controller_spec.rb

@@ -135,6 +135,10 @@ describe Projects::MilestonesController do
   end
 
   describe "#destroy" do
+    before do
+      stub_feature_flags(track_resource_milestone_change_events: false)
+    end
+
     it "removes milestone" do
       expect(issue.milestone_id).to eq(milestone.id)
 

spec/factories/resource_milestone_event.rb

+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :resource_milestone_event do
+    issue { merge_request.nil? ? create(:issue) : nil }
+    merge_request { nil }
+    milestone
+    action { :add }
+    state { :opened }
+    user { issue&.author || merge_request&.author || create(:user) }
+  end
+end

spec/lib/gitlab/import_export/all_models.yml

@@ -9,6 +9,7 @@ issues:
 - notes
 - resource_label_events
 - resource_weight_events
+- resource_milestone_events
 - sentry_issue
 - label_links
 - labels
@@ -109,6 +110,7 @@ merge_requests:
 - milestone
 - notes
 - resource_label_events
+- resource_milestone_events
 - label_links
 - labels
 - last_edited_by

spec/models/milestone_note_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe MilestoneNote do
+  describe '.from_event' do
+    let(:author) { create(:user) }
+    let(:project) { create(:project, :repository) }
+    let(:noteable) { create(:issue, author: author, project: project) }
+    let(:event) { create(:resource_milestone_event, issue: noteable) }
+
+    subject { described_class.from_event(event, resource: noteable, resource_parent: project) }
+
+    it_behaves_like 'a system note', exclude_project: true do
+      let(:action) { 'milestone' }
+    end
+  end
+end

spec/models/resource_milestone_event_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ResourceMilestoneEvent, type: :model do
+  it_behaves_like 'a resource event'
+  it_behaves_like 'a resource event for issues'
+  it_behaves_like 'a resource event for merge requests'
+
+  it_behaves_like 'having unique enum values'
+
+  describe 'associations' do
+    it { is_expected.to belong_to(:milestone) }
+  end
+
+  describe 'validations' do
+    context 'when issue and merge_request are both nil' do
+      subject { build(described_class.name.underscore.to_sym, issue: nil, merge_request: nil) }
+
+      it { is_expected.not_to be_valid }
+    end
+
+    context 'when issue and merge_request are both set' do
+      subject { build(described_class.name.underscore.to_sym, issue: build(:issue), merge_request: build(:merge_request)) }
+
+      it { is_expected.not_to be_valid }
+    end
+
+    context 'when issue is set' do
+      subject { create(described_class.name.underscore.to_sym, issue: create(:issue), merge_request: nil) }
+
+      it { is_expected.to be_valid }
+    end
+
+    context 'when merge_request is set' do
+      subject { create(described_class.name.underscore.to_sym, issue: nil, merge_request: create(:merge_request)) }
+
+      it { is_expected.to be_valid }
+    end
+  end
+
+  describe 'states' do
+    [Issue, MergeRequest].each do |klass|
+      klass.available_states.each do |state|
+        it "supports state #{state.first} for #{klass.name.underscore}" do
+          model = create(klass.name.underscore, state: state[0])
+          key = model.class.name.underscore
+          event = build(described_class.name.underscore.to_sym, key => model, state: model.state)
+
+          expect(event.state).to eq(state[0])
+        end
+      end
+    end
+  end
+end

spec/services/issuable/clone/attributes_rewriter_spec.rb

@@ -75,5 +75,47 @@ describe Issuable::Clone::AttributesRewriter do
 
       expect(new_issue.reload.milestone).to eq(milestone)
     end
+
+    context 'with existing milestone events' do
+      let!(:milestone1_project1) { create(:milestone, title: 'milestone1', project: project1) }
+      let!(:milestone2_project1) { create(:milestone, title: 'milestone2', project: project1) }
+      let!(:milestone3_project1) { create(:milestone, title: 'milestone3', project: project1) }
+
+      let!(:milestone1_project2) { create(:milestone, title: 'milestone1', project: project2) }
+      let!(:milestone2_project2) { create(:milestone, title: 'milestone2', project: project2) }
+
+      before do
+        original_issue.update(milestone: milestone2_project1)
+
+        create_event(milestone1_project1)
+        create_event(milestone2_project1)
+        create_event(milestone1_project1, 'remove')
+        create_event(milestone3_project1)
+      end
+
+      it 'copies existing resource milestone events' do
+        subject.execute
+
+        new_issue_milestone_events = new_issue.reload.resource_milestone_events
+        expect(new_issue_milestone_events.count).to eq(3)
+
+        expect_milestone_event(new_issue_milestone_events.first, milestone: milestone1_project2, action: 'add', state: 'opened')
+        expect_milestone_event(new_issue_milestone_events.second, milestone: milestone2_project2, action: 'add', state: 'opened')
+        expect_milestone_event(new_issue_milestone_events.third, milestone: milestone1_project2, action: 'remove', state: 'opened')
+      end
+
+      def create_event(milestone, action = 'add')
+        create(:resource_milestone_event, issue: original_issue, milestone: milestone, action: action)
+      end
+
+      def expect_milestone_event(event, expected_attrs)
+        expect(event.milestone_id).to eq(expected_attrs[:milestone].id)
+        expect(event.action).to eq(expected_attrs[:action])
+        expect(event.state).to eq(expected_attrs[:state])
+
+        expect(event.reference).to be_nil
+        expect(event.reference_html).to be_nil
+      end
+    end
   end
 end

spec/services/issuable/common_system_notes_service_spec.rb

@@ -3,8 +3,9 @@
 require 'spec_helper'
 
 describe Issuable::CommonSystemNotesService do
-  let(:user) { create(:user) }
-  let(:project) { create(:project) }
+  let_it_be(:project) { create(:project) }
+  let_it_be(:user) { create(:user) }
+
   let(:issuable) { create(:issue, project: project) }
 
   context 'on issuable update' do
@@ -35,6 +36,8 @@ describe Issuable::CommonSystemNotesService do
       before do
         milestone = create(:milestone, project: project)
         issuable.milestone_id = milestone.id
+
+        stub_feature_flags(track_resource_milestone_change_events: false)
       end
 
       it_behaves_like 'system note creation', {}, 'changed milestone'
@@ -97,12 +100,39 @@ describe Issuable::CommonSystemNotesService do
       expect(event.user_id).to eq user.id
     end
 
-    it 'creates a system note for milestone set' do
-      issuable.milestone = create(:milestone, project: project)
-      issuable.save
+    context 'when milestone change event tracking is disabled' do
+      before do
+        stub_feature_flags(track_resource_milestone_change_events: false)
 
-      expect { subject }.to change { issuable.notes.count }.from(0).to(1)
-      expect(issuable.notes.last.note).to match('changed milestone')
+        issuable.milestone = create(:milestone, project: project)
+        issuable.save
+      end
+
+      it 'creates a system note for milestone set' do
+        expect { subject }.to change { issuable.notes.count }.from(0).to(1)
+        expect(issuable.notes.last.note).to match('changed milestone')
+      end
+
+      it 'does not create a milestone change event' do
+        expect { subject }.not_to change { ResourceMilestoneEvent.count }
+      end
+    end
+
+    context 'when milestone change event tracking is enabled' do
+      let_it_be(:milestone) { create(:milestone, project: project) }
+      let_it_be(:issuable) { create(:issue, project: project, milestone: milestone) }
+
+      before do
+        stub_feature_flags(track_resource_milestone_change_events: true)
+      end
+
+      it 'does not create a system note for milestone set' do
+        expect { subject }.not_to change { issuable.notes.count }
+      end
+
+      it 'creates a milestone change event' do
+        expect { subject }.to change { ResourceMilestoneEvent.count }.from(0).to(1)
+      end
     end
 
     it 'creates a system note for due_date set' do

spec/services/issues/update_service_spec.rb

@@ -385,6 +385,10 @@ describe Issues::UpdateService, :mailer do
       end
 
       context 'when the milestone is removed' do
+        before do
+          stub_feature_flags(track_resource_milestone_change_events: false)
+        end
+
         let!(:non_subscriber) { create(:user) }
 
         let!(:subscriber) do
@@ -411,6 +415,10 @@ describe Issues::UpdateService, :mailer do
       end
 
       context 'when the milestone is changed' do
+        before do
+          stub_feature_flags(track_resource_milestone_change_events: false)
+        end
+
         let!(:non_subscriber) { create(:user) }
 
         let!(:subscriber) do

spec/services/merge_requests/update_service_spec.rb

@@ -367,6 +367,10 @@ describe MergeRequests::UpdateService, :mailer do
       end
 
       context 'when the milestone is removed' do
+        before do
+          stub_feature_flags(track_resource_milestone_change_events: false)
+        end
+
         let!(:non_subscriber) { create(:user) }
 
         let!(:subscriber) do
@@ -393,6 +397,10 @@ describe MergeRequests::UpdateService, :mailer do
       end
 
       context 'when the milestone is changed' do
+        before do
+          stub_feature_flags(track_resource_milestone_change_events: false)
+        end
+
         let!(:non_subscriber) { create(:user) }
 
         let!(:subscriber) do

spec/services/resource_events/change_milestone_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ResourceEvents::ChangeMilestoneService do
+  shared_examples 'milestone events creator' do
+    let_it_be(:user) { create(:user) }
+
+    let_it_be(:milestone) { create(:milestone) }
+
+    context 'when milestone is present' do
+      before do
+        resource.milestone = milestone
+      end
+
+      let(:service) { described_class.new(resource: resource, user: user, created_at: created_at_time) }
+
+      it 'creates the expected event record' do
+        expect { service.execute }.to change { ResourceMilestoneEvent.count }.from(0).to(1)
+
+        events = ResourceMilestoneEvent.all
+
+        expect(events.size).to eq(1)
+        expect_event_record(events.first, action: 'add', milestone: milestone, state: 'opened')
+      end
+    end
+
+    context 'when milestones is not present' do
+      before do
+        resource.milestone = nil
+      end
+
+      let(:service) { described_class.new(resource: resource, user: user, created_at: created_at_time) }
+
+      it 'creates the expected event records' do
+        expect { service.execute }.to change { ResourceMilestoneEvent.count }.from(0).to(1)
+
+        expect_event_record(ResourceMilestoneEvent.first, action: 'remove', milestone: nil, state: 'opened')
+      end
+    end
+
+    def expect_event_record(event, expected_attrs)
+      expect(event.action).to eq(expected_attrs[:action])
+      expect(event.state).to eq(expected_attrs[:state])
+      expect(event.user).to eq(user)
+      expect(event.issue).to eq(resource) if resource.is_a?(Issue)
+      expect(event.issue).to be_nil unless resource.is_a?(Issue)
+      expect(event.merge_request).to eq(resource) if resource.is_a?(MergeRequest)
+      expect(event.merge_request).to be_nil unless resource.is_a?(MergeRequest)
+      expect(event.milestone).to eq(expected_attrs[:milestone])
+      expect(event.created_at).to eq(created_at_time)
+    end
+  end
+
+  let_it_be(:merge_request) { create(:merge_request) }
+  let_it_be(:issue) { create(:issue) }
+
+  let!(:created_at_time) { Time.utc(2019, 12, 30) }
+
+  it_behaves_like 'milestone events creator' do
+    let(:resource) { issue }
+  end
+
+  it_behaves_like 'milestone events creator' do
+    let(:resource) { merge_request }
+  end
+end

spec/support/shared_examples/quick_actions/issue/move_quick_action_shared_examples.rb

@@ -50,6 +50,8 @@ RSpec.shared_examples 'move quick action' do
       let(:bug)      { create(:label, project: project, title: 'bug') }
       let(:wontfix)  { create(:label, project: project, title: 'wontfix') }
 
+      let!(:target_milestone) { create(:milestone, title: '1.0', project: target_project) }
+
       before do
         target_project.add_maintainer(user)
       end

spec/support/shared_examples/resource_events.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+shared_examples 'a resource event' do
+  let_it_be(:user1) { create(:user) }
+  let_it_be(:user2) { create(:user) }
+
+  let_it_be(:issue1) { create(:issue, author: user1) }
+  let_it_be(:issue2) { create(:issue, author: user1) }
+  let_it_be(:issue3) { create(:issue, author: user2) }
+
+  describe 'validations' do
+    it { is_expected.not_to allow_value(nil).for(:user) }
+  end
+
+  describe 'associations' do
+    it { is_expected.to belong_to(:user) }
+  end
+
+  describe '.created_after' do
+    let!(:created_at1) { 1.day.ago }
+    let!(:created_at2) { 2.days.ago }
+    let!(:created_at3) { 3.days.ago }
+
+    let!(:event1) { create(described_class.name.underscore.to_sym, issue: issue1, created_at: created_at1) }
+    let!(:event2) { create(described_class.name.underscore.to_sym, issue: issue2, created_at: created_at2) }
+    let!(:event3) { create(described_class.name.underscore.to_sym, issue: issue2, created_at: created_at3) }
+
+    it 'returns the expected events' do
+      events = described_class.created_after(created_at3)
+
+      expect(events).to contain_exactly(event1, event2)
+    end
+
+    it 'returns no events if time is after last record time' do
+      events = described_class.created_after(1.minute.ago)
+
+      expect(events).to be_empty
+    end
+  end
+end
+
+shared_examples 'a resource event for issues' do
+  let_it_be(:user1) { create(:user) }
+  let_it_be(:user2) { create(:user) }
+
+  let_it_be(:issue1) { create(:issue, author: user1) }
+  let_it_be(:issue2) { create(:issue, author: user1) }
+  let_it_be(:issue3) { create(:issue, author: user2) }
+
+  describe 'associations' do
+    it { is_expected.to belong_to(:issue) }
+  end
+
+  describe '.by_issue' do
+    let_it_be(:event1) { create(described_class.name.underscore.to_sym, issue: issue1) }
+    let_it_be(:event2) { create(described_class.name.underscore.to_sym, issue: issue2) }
+    let_it_be(:event3) { create(described_class.name.underscore.to_sym, issue: issue1) }
+
+    it 'returns the expected records for an issue with events' do
+      events = described_class.by_issue(issue1)
+
+      expect(events).to contain_exactly(event1, event3)
+    end
+
+    it 'returns the expected records for an issue with no events' do
+      events = described_class.by_issue(issue3)
+
+      expect(events).to be_empty
+    end
+  end
+end
+
+shared_examples 'a resource event for merge requests' do
+  let_it_be(:user1) { create(:user) }
+  let_it_be(:user2) { create(:user) }
+
+  let_it_be(:merge_request1) { create(:merge_request, author: user1) }
+  let_it_be(:merge_request2) { create(:merge_request, author: user1) }
+  let_it_be(:merge_request3) { create(:merge_request, author: user2) }
+
+  describe 'associations' do
+    it { is_expected.to belong_to(:merge_request) }
+  end
+
+  describe '.by_merge_request' do
+    let_it_be(:event1) { create(described_class.name.underscore.to_sym, merge_request: merge_request1) }
+    let_it_be(:event2) { create(described_class.name.underscore.to_sym, merge_request: merge_request2) }
+    let_it_be(:event3) { create(described_class.name.underscore.to_sym, merge_request: merge_request1) }
+
+    it 'returns the expected records for an issue with events' do
+      events = described_class.by_merge_request(merge_request1)
+
+      expect(events).to contain_exactly(event1, event3)
+    end
+
+    it 'returns the expected records for an issue with no events' do
+      events = described_class.by_merge_request(merge_request3)
+
+      expect(events).to be_empty
+    end
+  end
+end