Add integration test for user login
user
```ruby
require 'test_helper'

class UsersLoginTest < ActionDispatch::IntegrationTest
  test 'login with invalid information' do
    get login_path
    assert_template 'sessions/new'
    post login_path, session: {email: '', password: ''}
    assert_template 'sessions/new'
    assert_not flash.empty?
    # ensure flash doesn't persist for an extra pageload
    get login_path
    assert flash.empty?
  end
end
```
assistant