From: Philipp Meier <meier@...>
Date: 2002-10-04T01:44:20+09:00
Subject: Re: Reusing base classes tests?


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On Fri, Oct 04, 2002 at 01:26:01AM +0900, Phlip wrote:
> coma_killen@fastmail.fm wrote:
>=20
> > Whats the standard way to reuse the Test::Unit tests for a
> > base class when deriving a subclass? Should the testcase
> > class derive from the base class testcase class or are there
> > better ways?
>=20
> The best way I have found is to inherit, then create the testee in a meth=
od=20
> called 'warmUp'. Then override that method. Don't call 'warmUp' from=20
> 'initialize'.
>=20
> This page does not contain enough:
>=20
>         http://c2.com/cgi/wiki?AbstractTest
>=20
> Test rigs are pragmatic, not magic. Put another way, Liskov Substitution=
=20
> Principle applies between the base and derived test, so the system should=
=20
> >not< be able to tell the difference between a test method that calls=20
> 'warmUp' and one that does not. LSP in the tests does not mean everyone=
=20
> must call 'warmUp'.
>=20
> Classes, however, should follow LSP, so tests a base class should pass th=
e=20
> derived class should pass too.

I think I lost you here. Assume the following

class Vehicle
end

class Car
	def wheels
		return 4
	end
end

class Truck
	def wheels
		return 8
	end
end

class CarTest
	def test_wheels
		assert_equal(4,testee.wheels)
	end
end

How should Truck pass CarTest? Or should TruckTest inherite from CarTest
and override test_wheels? Whould this be according to LSP?

-billy.

--=20
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