Allow avatar_icon to operate on a User

If the User object is already known before calling this method being
able to re-use said object can save us an extra SQL query.

app/helpers/application_helper.rb

@@ -68,13 +68,17 @@ module ApplicationHelper
     end
   end
 
-  def avatar_icon(user_email = '', size = nil)
-    user = User.find_by(email: user_email)
+  def avatar_icon(user_or_email = nil, size = nil)
+    if user_or_email.is_a?(User)
+      user = user_or_email
+    else
+      user = User.find_by(email: user_or_email)
+    end
 
     if user
       user.avatar_url(size) || default_avatar
     else
-      gravatar_icon(user_email, size)
+      gravatar_icon(user_or_email, size)
     end
   end
 

spec/helpers/application_helper_spec.rb

@@ -99,6 +99,15 @@ describe ApplicationHelper do
 
       helper.avatar_icon('foo@example.com', 20)
     end
+
+    describe 'using a User' do
+      it 'should return an URL for the avatar' do
+        user = create(:user, avatar: File.open(avatar_file_path))
+
+        expect(helper.avatar_icon(user).to_s).
+          to match("/uploads/user/avatar/#{user.id}/banana_sample.gif")
+      end
+    end
   end
 
   describe 'gravatar_icon' do