like spec, don't make so many photso

spec/models/like_spec.rb

@@ -5,6 +5,7 @@ require 'rails_helper'
 describe 'like' do
   let(:member) { FactoryBot.create(:member) }
   let(:post)   { FactoryBot.create(:post)   }
+  let(:photo)  { FactoryBot.create :photo }
 
   context 'existing like' do
     before do
@@ -61,4 +62,14 @@ describe 'like' do
     member.destroy
     expect(Like.all).not_to include like
   end
+
+  it 'liked_by_members_names' do
+    expect(post.liked_by_members_names).to eq []
+    Like.create(member: member, likeable: post)
+    expect(post.liked_by_members_names).to eq [member.login_name]
+
+    expect(photo.liked_by_members_names).to eq []
+    Like.create(member: member, likeable: photo)
+    expect(photo.liked_by_members_names).to eq [member.login_name]
+  end
 end