fatvegan

The assert_difference test method in Rails is nice, but I found myself wanting a bit more flexibility. Like passing arguments to the method, not having to specify the exact change and checking for changes to things apart from numbers. So I wrote this. It gives you assert_change and assert_no_change which really just run the same thing twice. You could use a lambda sort of thing instead, which might be clearer. And it probably needs some kind of way of attaching a message. But I am mostly happy with it.

module Test::Unit::AssertChangeHelper
  def assert_change(object, *args, &block)
    old, new = before_and_after(object, *args, &block)
    assert_not_equal old, new
  end

  def assert_no_change(object, *args, &block)
    old, new = before_and_after(object, *args, &block)
    assert_equal old, new
  end

  protected
  def before_and_after(object, *args, &block)
    old = object.send(*args)
    block.call
    new = object.send(*args)
    return old, new
  end
end

You would use it like this:

assert_change(Visit, :find, :all, :conditions => ['is_exception = 1']) do
  Visit.create(options)
end