things_controller.rb

class ThingsController < ApplicationController
  class UnRescuedError < StandardError; end
  class RescuedError < StandardError; end
  
  rescue_from RescuedError do |exception|
    #no-op
  end
  
  def action_that_raises_rescued_error
    raise RescuedError
  end
  
  def action_that_raises_un_rescued_error
    raise UnRescuedError
  end
  
end

things_controller_test.output

$ ruby test/functional/things_controller_test.rb 
Loaded suite test/functional/things_controller_test
Started
....
Finished in 0.198612 seconds.

4 tests, 5 assertions, 0 failures, 0 errors

things_controller_test.rb

require File.join(File.dirname(__FILE__), "/../test_helper")

class ThingsControllerTest < ActionController::TestCase
  
  test "action_that_raises_rescued_error does not raise error" do
    get :action_that_raises_rescued_error
    assert_response 200
  end

  test "action_that_raises_rescued_error does not raise error with rescue_action_in_public!" do
    rescue_action_in_public!
    get :action_that_raises_rescued_error
    assert_response 200
  end

  test "action_that_raises_un_rescued_error raises error in test" do
    assert_raises ThingsController::UnRescuedError do
      get :action_that_raises_un_rescued_error
    end
    assert_response 200 # just to see what rails does here - wouldn't do this normally
  end

  test "action_that_raises_un_rescued_error raises error in response" do
    rescue_action_in_public!
    get :action_that_raises_un_rescued_error
    assert_response 500
  end

end