FIX: Group owners should be able to invite users to their groups.

https://meta.discourse.org/t/group-owner-cannot-send-an-invite-to-a-group/60617/12

spec/serializers/basic_group_user_serializer_spec.rb

@@ -0,0 +1,36 @@
+require 'rails_helper'
+
+describe BasicGroupUserSerializer do
+  let(:group) { Fabricate(:group) }
+  let(:user) { Fabricate(:user) }
+
+  before do
+    group.add(user)
+  end
+
+  describe '#owner' do
+    describe 'when scoped to the user' do
+      it 'should be false' do
+        json = described_class.new(
+          GroupUser.last,
+          scope: Guardian.new(user),
+          root: false
+        ).as_json
+
+        expect(json[:owner]).to eq(false)
+      end
+    end
+
+    describe 'when not scoped to the user' do
+      it 'should be nil' do
+        json = described_class.new(
+          GroupUser.last,
+          scope: Guardian.new,
+          root: false
+        ).as_json
+
+        expect(json[:owner]).to eq(nil)
+      end
+    end
+  end
+end