Add a SystemNoteService class

There's a lot of code in the Note model that only deals with creating
system notes, so we're going to split that into its own class.

app/models/concerns/mentionable.rb

@@ -39,7 +39,7 @@ module Mentionable
   # Determine whether or not a cross-reference Note has already been created between this Mentionable and
   # the specified target.
   def has_mentioned?(target)
-    Note.cross_reference_exists?(target, local_reference)
+    SystemNoteService.cross_reference_exists?(target, local_reference)
   end
 
   def mentioned_users(current_user = nil, p = project)

app/models/note.rb

@@ -63,143 +63,9 @@ class Note < ActiveRecord::Base
   after_update :set_references
 
   class << self
-    def create_status_change_note(noteable, project, author, status, source)
-      body = "Status changed to #{status}#{' by ' + source.gfm_reference if source}"
-
-      create(
-        noteable: noteable,
-        project: project,
-        author: author,
-        note: body,
-        system: true
-      )
-    end
-
-    # +noteable+ was referenced from +mentioner+, by including GFM in either
-    # +mentioner+'s description or an associated Note.
-    # Create a system Note associated with +noteable+ with a GFM back-reference
-    # to +mentioner+.
-    def create_cross_reference_note(noteable, mentioner, author)
-      gfm_reference = mentioner_gfm_ref(noteable, mentioner)
-
-      note_options = {
-        project: noteable.project,
-        author: author,
-        note: cross_reference_note_content(gfm_reference),
-        system: true
-      }
-
-      if noteable.kind_of?(Commit)
-        note_options.merge!(noteable_type: 'Commit', commit_id: noteable.id)
-      else
-        note_options.merge!(noteable: noteable)
-      end
-
-      create(note_options) unless cross_reference_disallowed?(noteable, mentioner)
-    end
-
-    def create_milestone_change_note(noteable, project, author, milestone)
-      body = if milestone.nil?
-               'Milestone removed'
-             else
-               "Milestone changed to #{milestone.title}"
-             end
-
-      create(
-        noteable: noteable,
-        project: project,
-        author: author,
-        note: body,
-        system: true
-      )
-    end
-
-    def create_assignee_change_note(noteable, project, author, assignee)
-      body = assignee.nil? ? 'Assignee removed' : "Reassigned to @#{assignee.username}"
-
-      create({
-        noteable: noteable,
-        project: project,
-        author: author,
-        note: body,
-        system: true
-      })
-    end
-
-    def create_labels_change_note(noteable, project, author, added_labels, removed_labels)
-      labels_count = added_labels.count + removed_labels.count
-      added_labels = added_labels.map{ |label| "~#{label.id}" }.join(' ')
-      removed_labels = removed_labels.map{ |label| "~#{label.id}" }.join(' ')
-      message = ''
-
-      if added_labels.present?
-        message << "added #{added_labels}"
-      end
-
-      if added_labels.present? && removed_labels.present?
-        message << ' and '
-      end
-
-      if removed_labels.present?
-        message << "removed #{removed_labels}"
-      end
-
-      message << ' ' << 'label'.pluralize(labels_count)
-      body = "#{message.capitalize}"
-
-      create(
-        noteable: noteable,
-        project: project,
-        author: author,
-        note: body,
-        system: true
-      )
-    end
-
-    def create_new_commits_note(merge_request, project, author, new_commits, existing_commits = [], oldrev = nil)
-      total_count = new_commits.length + existing_commits.length
-      commits_text = ActionController::Base.helpers.pluralize(total_count, 'commit')
-      body = "Added #{commits_text}:\n\n"
-
-      if existing_commits.length > 0
-        commit_ids =
-          if existing_commits.length == 1
-            existing_commits.first.short_id
-          else
-            if oldrev
-              "#{Commit.truncate_sha(oldrev)}...#{existing_commits.last.short_id}"
-            else
-              "#{existing_commits.first.short_id}..#{existing_commits.last.short_id}"
-            end
-          end
-
-        commits_text = ActionController::Base.helpers.pluralize(existing_commits.length, 'commit')
-
-        branch =
-          if merge_request.for_fork?
-            "#{merge_request.target_project_namespace}:#{merge_request.target_branch}"
-          else
-            merge_request.target_branch
-          end
-
-        message = "* #{commit_ids} - #{commits_text} from branch `#{branch}`"
-        body << message
-        body << "\n"
-      end
-
-      new_commits.each do |commit|
-        message = "* #{commit.short_id} - #{commit.title}"
-        body << message
-        body << "\n"
-      end
-
-      create(
-        noteable: merge_request,
-        project: project,
-        author: author,
-        note: body,
-        system: true
-      )
+    # TODO (rspeicher): Update usages
+    def create_cross_reference_note(*args)
+      SystemNoteService.cross_reference(*args)
     end
 
     def discussions_from_notes(notes)
@@ -227,88 +93,19 @@ class Note < ActiveRecord::Base
       [:discussion, type.try(:underscore), id, line_code].join("-").to_sym
     end
 
-    # Determine if cross reference note should be created.
-    # eg. mentioning a commit in MR comments which exists inside a MR
-    # should not create "mentioned in" note.
-    def cross_reference_disallowed?(noteable, mentioner)
-      if mentioner.kind_of?(MergeRequest)
-        mentioner.commits.map(&:id).include? noteable.id
-      end
-    end
-
-    # Determine whether or not a cross-reference note already exists.
-    def cross_reference_exists?(noteable, mentioner)
-      gfm_reference = mentioner_gfm_ref(noteable, mentioner, true)
-      notes = if noteable.is_a?(Commit)
-                where(commit_id: noteable.id, noteable_type: 'Commit')
-              else
-                where(noteable_id: noteable.id, noteable_type: noteable.class)
-              end
-
-      notes.where('note like ?', cross_reference_note_pattern(gfm_reference)).
-        system.any?
-    end
-
     def search(query)
       where("note like :query", query: "%#{query}%")
     end
-
-    def cross_reference_note_prefix
-      'mentioned in '
-    end
-
-    private
-
-    def cross_reference_note_content(gfm_reference)
-      cross_reference_note_prefix + "#{gfm_reference}"
-    end
-
-    def cross_reference_note_pattern(gfm_reference)
-      # Older cross reference notes contained underscores for emphasis
-      "%" + cross_reference_note_content(gfm_reference) + "%"
-    end
-
-    # Prepend the mentioner's namespaced project path to the GFM reference for
-    # cross-project references.  For same-project references, return the
-    # unmodified GFM reference.
-    def mentioner_gfm_ref(noteable, mentioner, cross_reference = false)
-      if mentioner.is_a?(Commit) && cross_reference
-        return mentioner.gfm_reference.sub('commit ', 'commit %')
-      end
-      
-      full_gfm_reference(mentioner.project, noteable.project, mentioner)
   end
 
-    # Return the +mentioner+ GFM reference.  If the mentioner and noteable
-    # projects are not the same, add the mentioning project's path to the
-    # returned value.
-    def full_gfm_reference(mentioning_project, noteable_project, mentioner)
-      if mentioning_project == noteable_project
-        mentioner.gfm_reference
-      else
-        if mentioner.is_a?(Commit)
-          mentioner.gfm_reference.sub(
-            /(commit )/,
-            "\\1#{mentioning_project.path_with_namespace}@"
-          )
-        else
-          mentioner.gfm_reference.sub(
-            /(issue |merge request )/,
-            "\\1#{mentioning_project.path_with_namespace}"
-          )
-        end
-      end
-    end
+  def cross_reference?
+    SystemNoteService.cross_reference?(note)
   end
 
   def max_attachment_size
     current_application_settings.max_attachment_size.megabytes.to_i
   end
 
-  def cross_reference?
-    note.start_with?(self.class.cross_reference_note_prefix)
-  end
-
   def find_diff
     return nil unless noteable && noteable.diffs.present?
 

app/services/issuable_base_service.rb

@@ -2,17 +2,17 @@ class IssuableBaseService < BaseService
   private
 
   def create_assignee_note(issuable)
-    Note.create_assignee_change_note(
+    SystemNoteService.assignee_change(
       issuable, issuable.project, current_user, issuable.assignee)
   end
 
   def create_milestone_note(issuable)
-    Note.create_milestone_change_note(
+    SystemNoteService.milestone_change(
       issuable, issuable.project, current_user, issuable.milestone)
   end
 
   def create_labels_note(issuable, added_labels, removed_labels)
-    Note.create_labels_change_note(
+    SystemNoteService.label_change(
       issuable, issuable.project, current_user, added_labels, removed_labels)
   end
 end

app/services/issues/close_service.rb

@@ -14,7 +14,7 @@ module Issues
     private
 
     def create_note(issue, current_commit)
-      Note.create_status_change_note(issue, issue.project, current_user, issue.state, current_commit)
+      SystemNoteService.status_change(issue, issue.project, current_user, issue.state, current_commit)
     end
   end
 end

app/services/issues/reopen_service.rb

@@ -14,7 +14,7 @@ module Issues
     private
 
     def create_note(issue)
-      Note.create_status_change_note(issue, issue.project, current_user, issue.state, nil)
+      SystemNoteService.status_change(issue, issue.project, current_user, issue.state, nil)
     end
   end
 end

app/services/merge_requests/base_service.rb

@@ -2,7 +2,7 @@ module MergeRequests
   class BaseService < ::IssuableBaseService
 
     def create_note(merge_request)
-      Note.create_status_change_note(merge_request, merge_request.target_project, current_user, merge_request.state, nil)
+      SystemNoteService.status_change(merge_request, merge_request.target_project, current_user, merge_request.state, nil)
     end
 
     def hook_data(merge_request, action)

app/services/merge_requests/refresh_service.rb

@@ -82,8 +82,9 @@ module MergeRequests
           mr_commit_ids.include?(commit.id)
         end
 
-        Note.create_new_commits_note(merge_request, merge_request.project,
-                                     @current_user, new_commits, existing_commits, @oldrev)
+        SystemNoteService.commit_add(merge_request, merge_request.project,
+                                     @current_user, new_commits,
+                                     existing_commits, @oldrev)
       end
     end
 

app/services/system_note_service.rb

+# SystemNoteService
+#
+# Used for creating system notes (e.g., when a user references a merge request
+# from an issue, an issue's assignee changes, an issue is closed, etc.)
+#
+# All methods creating notes should be named using a singular noun and
+# present-tense verb (e.g., "assignee_change" not "assignee_changed",
+# "label_change" not "labels_change").
+class SystemNoteService
+  # Called when the assignee of a Noteable is changed or removed
+  #
+  # noteable - Noteable object
+  # project  - Project owning noteable
+  # author   - User performing the change
+  # assignee - User being assigned, or nil
+  #
+  # Example Note text:
+  #
+  #   "Assignee removed"
+  #
+  #   "Reassigned to @rspeicher"
+  #
+  # Returns the created Note object
+  def self.assignee_change(noteable, project, author, assignee)
+    body = assignee.nil? ? 'Assignee removed' : "Reassigned to @#{assignee.username}"
+
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
+  # Called when a Mentionable references a Noteable
+  #
+  # noteable  - Noteable object being referenced
+  # mentioner - Mentionable object
+  # author    - User performing the reference
+  #
+  # Example Note text:
+  #
+  #   "Mentioned in #1"
+  #
+  #   "Mentioned in !2"
+  #
+  #   "Mentioned in 54f7727c"
+  #
+  # See cross_reference_note_content.
+  #
+  # Returns the created Note object
+  def self.cross_reference(noteable, mentioner, author)
+    return if cross_reference_disallowed?(noteable, mentioner)
+
+    gfm_reference = mentioner_gfm_ref(noteable, mentioner)
+
+    note_options = {
+      project: noteable.project,
+      author:  author,
+      note:    cross_reference_note_content(gfm_reference)
+    }
+
+    if noteable.kind_of?(Commit)
+      note_options.merge!(noteable_type: 'Commit', commit_id: noteable.id)
+    else
+      note_options.merge!(noteable: noteable)
+    end
+
+    create_note(note_options)
+  end
+
+  # Called when one or more labels on a Noteable are added and/or removed
+  #
+  # noteable       - Noteable object
+  # project        - Project owning noteable
+  # author         - User performing the change
+  # added_labels   - Array of Labels added
+  # removed_labels - Array of Labels removed
+  #
+  # Example Note text:
+  #
+  #   "Added ~1 and removed ~2 ~3 labels"
+  #
+  #   "Added ~4 label"
+  #
+  #   "Removed ~5 label"
+  #
+  # Returns the created Note object
+  def self.label_change(noteable, project, author, added_labels, removed_labels)
+    labels_count = added_labels.count + removed_labels.count
+
+    references     = ->(label) { "~#{label.id}" }
+    added_labels   = added_labels.map(&references).join(' ')
+    removed_labels = removed_labels.map(&references).join(' ')
+
+    body = ''
+
+    if added_labels.present?
+      body << "added #{added_labels}"
+      body << ' and ' if removed_labels.present?
+    end
+
+    if removed_labels.present?
+      body << "removed #{removed_labels}"
+    end
+
+    body << ' ' << 'label'.pluralize(labels_count)
+    body = "#{body.capitalize}"
+
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
+  # Called when the milestone of a Noteable is changed
+  #
+  # noteable  - Noteable object
+  # project   - Project owning noteable
+  # author    - User performing the change
+  # milestone - Milestone being assigned, or nil
+  #
+  # Example Note text:
+  #
+  #   "Milestone removed"
+  #
+  #   "Miletone changed to 7.11"
+  #
+  # Returns the created Note object
+  def self.milestone_change(noteable, project, author, milestone)
+    body = 'Milestone '
+    body += milestone.nil? ? 'removed' : "changed to #{milestone.title}"
+
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
+  # Called when commits are added to a Merge Request
+  #
+  # noteable         - Noteable object
+  # project          - Project owning noteable
+  # author           - User performing the change
+  # new_commits      - Array of Commits added since last push
+  # existing_commits - Array of Commits added in a previous push
+  # oldrev           - TODO (rspeicher): I have no idea what this actually does
+  #
+  # See new_commit_summary and existing_commit_summary.
+  #
+  # Returns the created Note object
+  def self.commit_add(noteable, project, author, new_commits, existing_commits = [], oldrev = nil)
+    total_count  = new_commits.length + existing_commits.length
+    commits_text = "#{total_count} commit".pluralize(total_count)
+
+    body = "Added #{commits_text}:\n\n"
+    body << existing_commit_summary(noteable, existing_commits, oldrev)
+    body << new_commit_summary(new_commits).join("\n")
+
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
+  # Called when the status of a Noteable is changed
+  #
+  # noteable - Noteable object
+  # project  - Project owning noteable
+  # author   - User performing the change
+  # status   - String status
+  # source   - Mentionable performing the change, or nil
+  #
+  # Example Note text:
+  #
+  #   "Status changed to merged"
+  #
+  #   "Status changed to closed by bc17db76"
+  #
+  # Returns the created Note object
+  def self.status_change(noteable, project, author, status, source)
+    body = "Status changed to #{status}"
+    body += " by #{source.gfm_reference}" if source
+
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
+  def self.cross_reference?(note_text)
+    note_text.start_with?(cross_reference_note_prefix)
+  end
+
+  # Determine if cross reference note should be created.
+  # eg. mentioning a commit in MR comments which exists inside a MR
+  # should not create "mentioned in" note.
+  def self.cross_reference_disallowed?(noteable, mentioner)
+    if mentioner.kind_of?(MergeRequest)
+      mentioner.commits.map(&:id).include? noteable.id
+    end
+  end
+
+  def self.cross_reference_exists?(noteable, mentioner)
+    # Initial scope should be system notes of this noteable type
+    notes = Note.system.where(noteable_type: noteable.class)
+
+    if noteable.is_a?(Commit)
+      # Commits have non-integer IDs, so they're stored in `commit_id`
+      notes = notes.where(commit_id: noteable.id)
+    else
+      notes = notes.where(noteable_id: noteable.id)
+    end
+
+    gfm_reference = mentioner_gfm_ref(noteable, mentioner, true)
+    notes = notes.where('note like ?', cross_reference_note_pattern(gfm_reference))
+
+    notes.count > 0
+  end
+
+  private
+
+  def self.create_note(args = {})
+    Note.create(args.merge(system: true))
+  end
+
+  def self.cross_reference_note_prefix
+    'mentioned in '
+  end
+
+  # Prepend the mentioner's namespaced project path to the GFM reference for
+  # cross-project references.  For same-project references, return the
+  # unmodified GFM reference.
+  def self.mentioner_gfm_ref(noteable, mentioner, cross_reference = false)
+    if mentioner.is_a?(Commit) && cross_reference
+      return mentioner.gfm_reference.sub('commit ', 'commit %')
+    end
+
+    full_gfm_reference(mentioner.project, noteable.project, mentioner)
+  end
+
+  # Return the +mentioner+ GFM reference.  If the mentioner and noteable
+  # projects are not the same, add the mentioning project's path to the
+  # returned value.
+  def self.full_gfm_reference(mentioning_project, noteable_project, mentioner)
+    if mentioning_project == noteable_project
+      mentioner.gfm_reference
+    else
+      if mentioner.is_a?(Commit)
+        mentioner.gfm_reference.sub(
+          /(commit )/,
+          "\\1#{mentioning_project.path_with_namespace}@"
+        )
+      else
+        mentioner.gfm_reference.sub(
+          /(issue |merge request )/,
+          "\\1#{mentioning_project.path_with_namespace}"
+        )
+      end
+    end
+  end
+
+  def self.cross_reference_note_content(gfm_reference)
+    cross_reference_note_prefix + "#{gfm_reference}"
+  end
+
+  def self.cross_reference_note_pattern(gfm_reference)
+    # Older cross reference notes contained underscores for emphasis
+    "%" + cross_reference_note_content(gfm_reference) + "%"
+  end
+
+  # Build an Array of lines detailing each commit added in a merge request
+  #
+  # new_commits - Array of new Commit objects
+  #
+  # Returns an Array of Strings
+  def self.new_commit_summary(new_commits)
+    new_commits.collect do |commit|
+      "* #{commit.short_id} - #{commit.title}"
+    end
+  end
+
+  # Build a single line summarizing existing commits being added in a merge
+  # request
+  #
+  # noteable         - MergeRequest object
+  # existing_commits - Array of existing Commit objects
+  # oldrev           - Optional String SHA of ... TODO (rspeicher): I have no idea what this actually does.
+  #
+  # Examples:
+  #
+  #   "* ea0f8418...2f4426b7 - 24 commits from branch `master`"
+  #
+  #   "* ea0f8418..4188f0ea - 15 commits from branch `fork:master`"
+  #
+  #   "* ea0f8418 - 1 commit from branch `feature`"
+  #
+  # Returns a newline-terminated String
+  def self.existing_commit_summary(noteable, existing_commits, oldrev = nil)
+    return '' if existing_commits.empty?
+
+    count = existing_commits.size
+
+    commit_ids = if count == 1
+                   existing_commits.first.short_id
+                 else
+                   if oldrev
+                     "#{Commit.truncate_sha(oldrev)}...#{existing_commits.last.short_id}"
+                   else
+                     "#{existing_commits.first.short_id}..#{existing_commits.last.short_id}"
+                   end
+                 end
+
+    commits_text = "#{count} commit".pluralize(count)
+
+    branch = noteable.target_branch
+    branch = "#{noteable.target_project_namespace}:#{branch}" if noteable.for_fork?
+
+    "* #{commit_ids} - #{commits_text} from branch `#{branch}`\n"
+  end
+end

spec/factories/notes.rb

@@ -31,6 +31,7 @@ FactoryGirl.define do
     factory :note_on_merge_request,      traits: [:on_merge_request]
     factory :note_on_merge_request_diff, traits: [:on_merge_request, :on_diff]
     factory :note_on_project_snippet,    traits: [:on_project_snippet]
+    factory :system_note,                traits: [:system]
 
     trait :on_commit do
       project factory: :project
@@ -58,6 +59,10 @@ FactoryGirl.define do
       noteable_type "Snippet"
     end
 
+    trait :system do
+      system true
+    end
+
     trait :with_attachment do
       attachment { fixture_file_upload(Rails.root + "spec/fixtures/dk.png", "`/png") }
     end

spec/models/note_spec.rb

@@ -150,178 +150,6 @@ describe Note do
     end
   end
 
-  describe '#create_status_change_note' do
-    let(:project) { create(:project) }
-    let(:thing) { create(:issue, project: project) }
-    let(:author) { create(:user) }
-    let(:status) { 'new_status' }
-
-    subject { Note.create_status_change_note(thing, project, author, status, nil) }
-
-    it 'creates and saves a Note' do
-      is_expected.to be_a Note
-      expect(subject.id).not_to be_nil
-    end
-
-    describe '#noteable' do
-      subject { super().noteable }
-      it { is_expected.to eq(thing) }
-    end
-
-    describe '#project' do
-      subject { super().project }
-      it { is_expected.to eq(thing.project) }
-    end
-
-    describe '#author' do
-      subject { super().author }
-      it { is_expected.to eq(author) }
-    end
-
-    describe '#note' do
-      subject { super().note }
-      it { is_expected.to eq("Status changed to #{status}") }
-    end
-
-    it 'appends a back-reference if a closing mentionable is supplied' do
-      commit = double('commit', gfm_reference: 'commit 123456')
-      n = Note.create_status_change_note(thing, project, author, status, commit)
-
-      expect(n.note).to eq("Status changed to #{status} by commit 123456")
-    end
-  end
-
-  describe '#create_assignee_change_note' do
-    let(:project) { create(:project) }
-    let(:thing) { create(:issue, project: project) }
-    let(:author) { create(:user) }
-    let(:assignee) { create(:user, username: "assigned_user") }
-
-    subject { Note.create_assignee_change_note(thing, project, author, assignee) }
-
-    context 'creates and saves a Note' do
-      it { is_expected.to be_a Note }
-
-      describe '#id' do
-        subject { super().id }
-        it { is_expected.not_to be_nil }
-      end
-    end
-
-    describe '#noteable' do
-      subject { super().noteable }
-      it { is_expected.to eq(thing) }
-    end
-
-    describe '#project' do
-      subject { super().project }
-      it { is_expected.to eq(thing.project) }
-    end
-
-    describe '#author' do
-      subject { super().author }
-      it { is_expected.to eq(author) }
-    end
-
-    describe '#note' do
-      subject { super().note }
-      it { is_expected.to eq('Reassigned to @assigned_user') }
-    end
-
-    context 'assignee is removed' do
-      let(:assignee) { nil }
-
-      describe '#note' do
-        subject { super().note }
-        it { is_expected.to eq('Assignee removed') }
-      end
-    end
-  end
-
-  describe '#create_labels_change_note' do
-    let(:project) { create(:project) }
-    let(:thing) { create(:issue, project: project) }
-    let(:author) { create(:user) }
-    let(:label1) { create(:label) }
-    let(:label2) { create(:label) }
-    let(:added_labels) { [label1, label2] }
-    let(:removed_labels) { [] }
-
-    subject { Note.create_labels_change_note(thing, project, author, added_labels, removed_labels) }
-
-    context 'creates and saves a Note' do
-      it { is_expected.to be_a Note }
-
-      describe '#id' do
-        subject { super().id }
-        it { is_expected.not_to be_nil }
-      end
-    end
-
-    describe '#noteable' do
-      subject { super().noteable }
-      it { is_expected.to eq(thing) }
-    end
-
-    describe '#project' do
-      subject { super().project }
-      it { is_expected.to eq(thing.project) }
-    end
-
-    describe '#author' do
-      subject { super().author }
-      it { is_expected.to eq(author) }
-    end
-
-    describe '#note' do
-      subject { super().note }
-      it { is_expected.to eq("Added ~#{label1.id} ~#{label2.id} labels") }
-    end
-
-    context 'label is removed' do
-      let(:added_labels) { [label1]  }
-      let(:removed_labels) { [label2] }
-
-      describe '#note' do
-        subject { super().note }
-        it { is_expected.to eq("Added ~#{label1.id} and removed ~#{label2.id} labels") }
-      end
-    end
-  end
-
-  describe '#create_milestone_change_note' do
-    let(:project) { create(:project) }
-    let(:thing) { create(:issue, project: project) }
-    let(:milestone) { create(:milestone, project: project, title: "first_milestone") }
-    let(:author) { create(:user) }
-
-    subject { Note.create_milestone_change_note(thing, project, author, milestone) }
-
-    context 'creates and saves a Note' do
-      it { is_expected.to be_a Note }
-
-      describe '#id' do
-        subject { super().id }
-        it { is_expected.not_to be_nil }
-      end
-    end
-
-    describe '#project' do
-      subject { super().project }
-      it { is_expected.to eq(thing.project) }
-    end
-
-    describe '#author' do
-      subject { super().author }
-      it { is_expected.to eq(author) }
-    end
-
-    describe '#note' do
-      subject { super().note }
-      it { is_expected.to eq("Milestone changed to first_milestone") }
-    end
-  end
-
   describe '#create_cross_reference_note' do
     let(:project)    { create(:project) }
     let(:author)     { create(:user) }
@@ -476,70 +304,6 @@ describe Note do
     end
   end
 
-  describe '#cross_reference_exists?' do
-    let(:project) { create :project }
-    let(:author) { create :user }
-    let(:issue) { create :issue }
-    let(:commit0) { project.commit }
-    let(:commit1) { project.commit('HEAD~2') }
-
-    before do
-      Note.create_cross_reference_note(issue, commit0, author)
-    end
-
-    it 'detects if a mentionable has already been mentioned' do
-      expect(Note.cross_reference_exists?(issue, commit0)).to be_truthy
-    end
-
-    it 'detects if a mentionable has not already been mentioned' do
-      expect(Note.cross_reference_exists?(issue, commit1)).to be_falsey
-    end
-
-    context 'commit on commit' do
-      before do
-        Note.create_cross_reference_note(commit0, commit1, author)
-      end
-
-      it { expect(Note.cross_reference_exists?(commit0, commit1)).to be_truthy }
-      it { expect(Note.cross_reference_exists?(commit1, commit0)).to be_falsey }
-    end
-
-    context 'legacy note with Markdown emphasis' do
-      let(:issue2) { create :issue, project: project }
-      let!(:note) do
-        create :note, system: true, noteable_id: issue2.id,
-                      noteable_type: "Issue", note: "_mentioned in issue " \
-                      "#{issue.project.path_with_namespace}##{issue.iid}_"
-      end
-
-      it 'detects if a mentionable with emphasis has been mentioned' do
-        expect(Note.cross_reference_exists?(issue2, issue)).to be_truthy
-      end
-    end
-  end
-
-  describe '#cross_references_with_underscores?' do
-    let(:project) { create :project, path: "first_project" }
-    let(:second_project) { create :project, path: "second_project" }
-
-    let(:author) { create :user }
-    let(:issue0) { create :issue, project: project }
-    let(:issue1) { create :issue, project: second_project }
-    let!(:note) { Note.create_cross_reference_note(issue0, issue1, author) }
-
-    it 'detects if a mentionable has already been mentioned' do
-      expect(Note.cross_reference_exists?(issue0, issue1)).to be_truthy
-    end
-
-    it 'detects if a mentionable has not already been mentioned' do
-      expect(Note.cross_reference_exists?(issue1, issue0)).to be_falsey
-    end
-
-    it 'detects that text has underscores' do
-      expect(note.note).to eq("mentioned in issue #{second_project.path_with_namespace}##{issue1.iid}")
-    end
-  end
-
   describe '#system?' do
     let(:project) { create(:project) }
     let(:issue)   { create(:issue, project: project) }
@@ -554,30 +318,10 @@ describe Note do
       expect(@note).not_to be_system
     end
 
-    it 'should identify status-change notes as system notes' do
-      @note = Note.create_status_change_note(issue, project, author, 'closed', nil)
-      expect(@note).to be_system
-    end
-
     it 'should identify cross-reference notes as system notes' do
       @note = Note.create_cross_reference_note(issue, other, author)
       expect(@note).to be_system
     end
-
-    it 'should identify assignee-change notes as system notes' do
-      @note = Note.create_assignee_change_note(issue, project, author, assignee)
-      expect(@note).to be_system
-    end
-
-    it 'should identify label-change notes as system notes' do
-      @note = Note.create_labels_change_note(issue, project, author, [label], [])
-      expect(@note).to be_system
-    end
-
-    it 'should identify milestone-change notes as system notes' do
-      @note = Note.create_milestone_change_note(issue, project, author, milestone)
-      expect(@note).to be_system
-    end
   end
 
   describe :authorization do

spec/services/system_note_service_spec.rb

+require 'spec_helper'
+
+describe SystemNoteService do
+  let(:project)  { create(:project) }
+  let(:author)   { create(:user) }
+  let(:noteable) { create(:issue, project: project) }
+
+  shared_examples_for 'a system note' do
+    it 'sets the noteable model' do
+      expect(subject.noteable).to eq noteable
+    end
+
+    it 'sets the project' do
+      expect(subject.project).to eq project
+    end
+
+    it 'sets the author' do
+      expect(subject.author).to eq author
+    end
+
+    it 'is a system note' do
+      expect(subject).to be_system
+    end
+  end
+
+  describe '.assignee_change' do
+    let(:assignee) { create(:user) }
+
+    subject { described_class.assignee_change(noteable, project, author, assignee) }
+
+    it_behaves_like 'a system note'
+
+    context 'when assignee added' do
+      it 'sets the note text' do
+        expect(subject.note).to eq "Reassigned to @#{assignee.username}"
+      end
+    end
+
+    context 'when assignee removed' do
+      let(:assignee) { nil }
+
+      it 'sets the note text' do
+        expect(subject.note).to eq 'Assignee removed'
+      end
+    end
+  end
+
+  describe '.cross_reference' do
+    let(:mentioner) { create(:issue, project: project) }
+
+    subject { described_class.cross_reference(noteable, mentioner, author) }
+
+    it_behaves_like 'a system note'
+
+    context 'when cross-reference disallowed' do
+      before do
+        expect(described_class).to receive(:cross_reference_disallowed?).and_return(true)
+      end
+
+      it 'returns nil' do
+        expect(subject).to be_nil
+      end
+    end
+
+    context 'when cross-reference allowed' do
+      before do
+        expect(described_class).to receive(:cross_reference_disallowed?).and_return(false)
+      end
+
+      describe 'note_body' do
+        context 'cross-project' do
+          let(:project2)  { create(:project) }
+          let(:mentioner) { create(:issue, project: project2) }
+
+          context 'from Commit' do
+            let(:mentioner) { project2.repository.commit }
+
+            it 'references the mentioning commit' do
+              expect(subject.note).to eq "mentioned in commit #{project2.path_with_namespace}@#{mentioner.id}"
+            end
+          end
+
+          context 'from non-Commit' do
+            it 'references the mentioning object' do
+              expect(subject.note).to eq "mentioned in issue #{project2.path_with_namespace}##{mentioner.iid}"
+            end
+          end
+        end
+
+        context 'same project' do
+          context 'from Commit' do
+            let(:mentioner) { project.repository.commit }
+
+            it 'references the mentioning commit' do
+              expect(subject.note).to eq "mentioned in commit #{mentioner.id}"
+            end
+          end
+
+          context 'from non-Commit' do
+            it 'references the mentioning object' do
+              expect(subject.note).to eq "mentioned in issue ##{mentioner.iid}"
+            end
+          end
+        end
+      end
+    end
+  end
+
+  describe '.label_change' do
+    let(:labels)  { create_list(:label, 2) }
+    let(:added)   { [] }
+    let(:removed) { [] }
+
+    subject { described_class.label_change(noteable, project, author, added, removed) }
+
+    it_behaves_like 'a system note'
+
+    context 'with added labels' do
+      let(:added)   { labels }
+      let(:removed) { [] }
+
+      it 'sets the note text' do
+        expect(subject.note).to eq "Added ~#{labels[0].id} ~#{labels[1].id} labels"
+      end
+    end
+
+    context 'with removed labels' do
+      let(:added)   { [] }
+      let(:removed) { labels }
+
+      it 'sets the note text' do
+        expect(subject.note).to eq "Removed ~#{labels[0].id} ~#{labels[1].id} labels"
+      end
+    end
+
+    context 'with added and removed labels' do
+      let(:added)   { [labels[0]] }
+      let(:removed) { [labels[1]] }
+
+      it 'sets the note text' do
+        expect(subject.note).to eq "Added ~#{labels[0].id} and removed ~#{labels[1].id} labels"
+      end
+    end
+  end
+
+  describe '.milestone_change' do
+    let(:milestone) { create(:milestone, project: project) }
+
+    subject { described_class.milestone_change(noteable, project, author, milestone) }
+
+    it_behaves_like 'a system note'
+
+    context 'when milestone added' do
+      it 'sets the note text' do
+        expect(subject.note).to eq "Milestone changed to #{milestone.title}"
+      end
+    end
+
+    context 'when milestone removed' do
+      let(:milestone) { nil }
+
+      it 'sets the note text' do
+        expect(subject.note).to eq 'Milestone removed'
+      end
+    end
+  end
+
+  describe '.commit_add' do
+    let(:noteable)    { create(:merge_request, source_project: project) }
+    let(:new_commits) { noteable.commits }
+    let(:old_commits) { [] }
+    let(:oldrev)      { nil }
+
+    subject { described_class.commit_add(noteable, project, author, new_commits, old_commits, oldrev) }
+
+    it_behaves_like 'a system note'
+
+    describe 'note body' do
+      let(:note_lines) { subject.note.split("\n").reject(&:blank?) }
+
+      context 'without existing commits' do
+        it 'adds a message header' do
+          expect(note_lines[0]).to eq "Added #{new_commits.size} commits:"
+        end
+
+        it 'adds a message line for each commit' do
+          new_commits.each_with_index do |commit, i|
+            # Skip the header
+            expect(note_lines[i + 1]).to eq "* #{commit.short_id} - #{commit.title}"
+          end
+        end
+      end
+
+      describe 'summary line for existing commits' do
+        let(:summary_line) { note_lines[1] }
+
+        context 'with one existing commit' do
+          let(:old_commits) { [noteable.commits.last] }
+
+          it 'includes the existing commit' do
+            expect(summary_line).to eq "* #{old_commits.first.short_id} - 1 commit from branch `feature`"
+          end
+        end
+
+        context 'with multiple existing commits' do
+          let(:old_commits) { noteable.commits[3..-1] }
+
+          context 'with oldrev' do
+            let(:oldrev) { noteable.commits[2].id }
+
+            it 'includes a commit range' do
+              expect(summary_line).to start_with "* #{Commit.truncate_sha(oldrev)}...#{old_commits.last.short_id}"
+            end
+
+            it 'includes a commit count' do
+              expect(summary_line).to end_with " - 2 commits from branch `feature`"
+            end
+          end
+
+          context 'without oldrev' do
+            it 'includes a commit range' do
+              expect(summary_line).to start_with "* #{old_commits[0].short_id}..#{old_commits[-1].short_id}"
+            end
+
+            it 'includes a commit count' do
+              expect(summary_line).to end_with " - 2 commits from branch `feature`"
+            end
+          end
+
+          context 'on a fork' do
+            before do
+              expect(noteable).to receive(:for_fork?).and_return(true)
+            end
+
+            it 'includes the project namespace' do
+              expect(summary_line).to end_with "`#{noteable.target_project_namespace}:feature`"
+            end
+          end
+        end
+      end
+    end
+  end
+
+  describe '.status_change' do
+    let(:status) { 'new_status' }
+    let(:source) { nil }
+
+    subject { described_class.status_change(noteable, project, author, status, source) }
+
+    it_behaves_like 'a system note'
+
+    context 'with a source' do
+      let(:source) { double('commit', gfm_reference: 'commit 123456') }
+
+      it 'sets the note text' do
+        expect(subject.note).to eq "Status changed to #{status} by commit 123456"
+      end
+    end
+
+    context 'without a source' do
+      it 'sets the note text' do
+        expect(subject.note).to eq "Status changed to #{status}"
+      end
+    end
+  end
+
+  describe '.cross_reference?' do
+    it 'is truthy when text begins with expected text' do
+      expect(described_class.cross_reference?('mentioned in issue #1')).to be_truthy
+    end
+
+    it 'is falsey when text does not begin with expected text' do
+      expect(described_class.cross_reference?('this is a note')).to be_falsey
+    end
+  end
+
+  describe '.cross_reference_disallowed?'
+
+  describe '.cross_reference_exists?' do
+    let(:commit0) { project.commit }
+    let(:commit1) { project.commit('HEAD~2') }
+
+    context 'issue from commit' do
+      before do
+        # Mention issue (noteable) from commit0
+        described_class.cross_reference(noteable, commit0, author)
+      end
+
+      it 'is truthy when already mentioned' do
+        expect(described_class.cross_reference_exists?(noteable, commit0)).
+          to be_truthy
+      end
+
+      it 'is falsey when not already mentioned' do
+        expect(described_class.cross_reference_exists?(noteable, commit1)).
+          to be_falsey
+      end
+    end
+
+    context 'commit from commit' do
+      before do
+        # Mention commit1 from commit0
+        described_class.cross_reference(commit0, commit1, author)
+      end
+
+      it 'is truthy when already mentioned' do
+        expect(described_class.cross_reference_exists?(commit0, commit1)).
+          to be_truthy
+      end
+
+      it 'is falsey when not already mentioned' do
+        expect(described_class.cross_reference_exists?(commit1, commit0)).
+          to be_falsey
+      end
+    end
+
+    context 'legacy note with Markdown emphasis' do
+      let(:mentioner) { create(:issue, project: project) }
+
+      before do
+        note = "_mentioned in issue ##{mentioner.iid}_"
+        create(:system_note, noteable: noteable, note: note, project: project)
+      end
+
+      it 'detects if a mentionable with emphasis has been mentioned' do
+        expect(described_class.cross_reference_exists?(noteable, mentioner)).
+          to be_truthy
+      end
+
+      context 'when referenced project has underscores' do
+        let(:project)  { create(:empty_project, path: 'first_project') }
+        let(:project2) { create(:empty_project, path: 'second_project') }
+
+        let(:issue)  { mentioner }
+        let(:issue2) { create(:issue, project: project2) }
+
+        before do
+          described_class.cross_reference(issue, issue2, author)
+        end
+
+        it 'is truthy when already mentioned' do
+          expect(described_class.cross_reference_exists?(issue, issue2)).
+            to be_truthy
+        end
+
+        it 'is falsey when not already mentioned' do
+          expect(described_class.cross_reference_exists?(issue2, issue)).
+            to be_falsey
+        end
+      end
+    end
+  end
+end