Asserts in Rails from models or controllers?

Is there a built-in way of specifying asserts in Rails that will throw an exception if an invariant is broken during development and testing?

Edit: Just to be clear, I'm looking for asserts that can be placed in models or controllers as opposed to asserts that you would use for unit tests.

From stackoverflow

• Beyond these, you mean?

  Gordon Wilson : I believe the OP is talking about asserts in the main code, as opposed to test assertions.

  Craig Stuntz : Hard to tell, isn't it? :)

  Gordon Wilson : a little, yeah ; )

  Readonly : Ah sorry about that. I've updated the question to be more clear.

• I don't believe there is. But, you can roll your own easily.

  Add something like this to environment.rb:

  class AssertFailure < Exception
  
  def assert
    if RAILS_ENV != 'production' && !yield
      raise AssertFailure
    end
  end
  

  Then, in your code, you can assert to your heart's content:

  assert { value == expected_value }
  

  If value does not equal expected_value and you aren't running in production, an exception will be raised.

• Raise exceptions, and use rescue_from.