add posts scope filter

spec/services/posts_query_resolver_serivce_spec.rb

@@ -0,0 +1,37 @@
+require 'rails_helper'
+
+RSpec.describe PostsQueryResolverService, type: :service do
+  context '#call' do
+    let(:current_user) { create(:user) }
+
+    context 'when without filter' do
+      it 'returns all posts' do
+        followed_user = create(:user)
+        create(:user_follow, follower_id: current_user.id, followed_id: followed_user.id)
+
+        post1 = create(:post, user_id: followed_user.id)
+        post2 = create(:post, user_id: followed_user.id)
+        post3 = create(:post)
+
+        expect(
+          described_class.call({}, current_user)
+        ).to eq([post1, post2, post3])
+      end
+    end
+
+    context 'when scoping by user follows' do
+      it 'returns only posts from user follows' do
+        followed_user = create(:user)
+        create(:user_follow, follower_id: current_user.id, followed_id: followed_user.id)
+
+        post1 = create(:post, user_id: followed_user.id)
+        post2 = create(:post, user_id: followed_user.id)
+        post3 = create(:post)
+
+        expect(
+          described_class.call({ scope: 'follows' }, current_user)
+        ).to eq([post1, post2])
+      end
+    end
+  end
+end