Add spec for Identity.find_for_oauth (#9441)

spec/models/identity_spec.rb

 require 'rails_helper'
 
 RSpec.describe Identity, type: :model do
-  pending "add some examples to (or delete) #{__FILE__}"
+  describe '.find_for_oauth' do
+    let(:auth) { Fabricate(:identity, user: Fabricate(:user)) }
+
+    it 'calls .find_or_create_by' do
+      expect(described_class).to receive(:find_or_create_by).with(uid: auth.uid, provider: auth.provider)
+      described_class.find_for_oauth(auth)
+    end
+
+    it 'returns an instance of Identity' do
+      expect(described_class.find_for_oauth(auth)).to be_instance_of Identity
+    end
+  end
 end