How to test 400 (bad request) error?

[Kris.S]

I'd like to write a spec for testing requests with invalid encoding parameters. The expected behaviour is that the 400 error page is rendered.

module ErrorResponses

  # See: https://github.com/rails/rails/pull/11289#issuecomment-118612393
  def respond_without_detailed_exceptions
    env_config = Rails.application.env_config
    original_show_exceptions = env_config["action_dispatch.show_exceptions"]
    original_show_detailed_exceptions = env_config["action_dispatch.show_detailed_exceptions"]
    env_config["action_dispatch.show_exceptions"] = true
    env_config["action_dispatch.show_detailed_exceptions"] = false
    yield
  ensure
    env_config["action_dispatch.show_exceptions"] = original_show_exceptions
    env_config["action_dispatch.show_detailed_exceptions"] = original_show_detailed_exceptions
  end
end

RSpec.configure do |config|
  config.include ErrorResponses
end

require 'rails_helper'

RSpec.describe 'Errors', type: :feature do
  around :each do |example|
    respond_without_detailed_exceptions do
      example.run
    end
  end

  context 'with invalid request parameter' do
    it 'renders 400' do
      visit '/home?test=%%aa%%'
      expect(page.status_code).to eq 400
    end
  end
end

The problem I'm having is that Rack would throw Rack::QueryParser::InvalidParameterError exception when calling visit '/home?test=%%aa%%', and the 400 error is never rendered from the spec.

Any help would be appreciated. Thanks.