How do I set HTTP_REFERER when testing in Rails?

The accepted answer doesn't work for integration tests because the @request variable doesn't exist.

According to RailsGuides, you can pass headers to the helpers.

Rails <= 4:

test "blah" do
  get root_path, {}, {'HTTP_REFERER' => 'http://foo.com'}
  ...
end

Rails >= 5:

test "blah" do
  get root_path, params: { id: 12 }, headers: { "HTTP_REFERER" => "http://foo.com" }
  ...
end

Their recommendation translates to the following:

setup do
  @request.env['HTTP_REFERER'] = 'http://test.com/sessions/new'
  post :create, { :user => { :email => 'invalid@abc' } }
end