Test that passing external host redirects to root
user
```ruby
# Copyright 2011-2018, The Trustees of Indiana University and Northwestern
#   University.  Licensed under the Apache License, Version 2.0 (the "License");
#   you may not use this file except in compliance with the License.
#
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#
# http://www.apache.org/licenses/LICENSE-2.0
#
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require 'rails_helper'

describe Users::OmniauthCallbacksController, type: :controller do
  before do
    @request.env["devise.mapping"] = Devise.mappings[:user]
  end

  describe '#find_user' do
    context 'when url param is present' do
      let(:user) { FactoryGirl.create(:user) }
      let(:params) {{ url: "http://other.host.com/a/sub/page" }}

      before do
        allow(User).to receive(:find_for_identity).and_return(user)
      end

      it 'redirects to homepage if url host does not match app host' do
        post :identity, params
        expect(response).to redirect_to(root_path)
      end
    end
  end
end
```
assistant