Add note for assignee changes

Change to username per @PixnBits suggestion

app/models/note.rb

@@ -82,6 +82,18 @@ def create_cross_reference_note(noteable, mentioner, author, project)
       }, without_protection: 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
+      }, without_protection: true)
+    end
+
     def discussions_from_notes(notes)
       discussion_ids = []
       discussions = []

app/observers/issue_observer.rb

@@ -19,6 +19,7 @@ def after_reopen(issue, transition)
   def after_update(issue)
     if issue.is_being_reassigned?
       notification.reassigned_issue(issue, current_user)
+      create_assignee_note(issue)
     end
 
     issue.notice_added_references(issue.project, current_user)
@@ -32,6 +33,10 @@ def create_note(issue)
     Note.create_status_change_note(issue, issue.project, current_user, issue.state, current_commit)
   end
 
+  def create_assignee_note(issue)
+    Note.create_assignee_change_note(issue, issue.project, current_user, issue.assignee)
+  end
+
   def execute_hooks(issue)
     issue.project.execute_hooks(issue.to_hook_data, :issue_hooks)
   end

spec/models/note_spec.rb

@@ -180,6 +180,31 @@
     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) }
+
+    subject { Note.create_assignee_change_note(thing, project, author, assignee) }
+
+    context 'creates and saves a Note' do
+      it { should be_a Note }
+      its(:id) { should_not be_nil }
+    end
+
+    its(:noteable) { should == thing }
+    its(:project) { should == thing.project }
+    its(:author) { should == author }
+    its(:note) { should =~ /Reassigned to @#{assignee.username}/ }
+
+    context 'assignee is removed' do
+      let(:assignee) { nil }
+
+      its(:note) { should =~ /Assignee removed/ }
+    end
+  end
+
   describe '#create_cross_reference_note' do
     let(:project)    { create(:project_with_code) }
     let(:author)     { create(:user) }
@@ -252,6 +277,7 @@
     let(:issue)   { create(:issue, project: project) }
     let(:other)   { create(:issue, project: project) }
     let(:author)  { create(:user) }
+    let(:assignee) { create(:user) }
 
     it 'should recognize user-supplied notes as non-system' do
       @note = create(:note_on_issue)
@@ -267,6 +293,11 @@
       @note = Note.create_cross_reference_note(issue, other, author, project)
       @note.should be_system
     end
+
+    it 'should identify assignee-change notes as system notes' do
+      @note = Note.create_assignee_change_note(issue, project, author, assignee)
+      @note.should be_system
+    end
   end
 
   describe :authorization do