From: Florian Gross <flgr@...>
Date: 2004-12-09T08:52:29+09:00
Subject: Re: Shield Pattern (was Re: Freezing Variable Assignment)

Eric Hodel wrote:

> On 08 Dec 2004, at 13:12, Nicholas Van Weerdenburg wrote:
>> Immutability also speaks to this- it's an interface contract that says
>> "read-only", limiting side effects. Having experienced the beauty of
>> making objects immutable and watching the   exceptions flare was a
>> epiphany for me in Java development.
> 
> I've used unit tests for this more that immutability.  Your same 
> euphoric state can be had with a solid, comprehensive set of unit 
> tests.  (Not to say that immutability can't help.)

I agree heavily with this. Specification by testing is a great way of 
ensuring that things work. Note that you can also state what things 
should *not* be allowed which can be just as important as testing that 
things are allowed and work correctly.

Unit testing in general leads you to decoupled components that you can 
swap out easily with Mocks (which means that in the real code you will 
be able to replace them with similar Objects that use the same 
interface) for ensuring that interfaces are used correctly. I'd like to 
recommend the "Test-driven development by example" book -- it explains 
well how to enforce code quality via tests because it uses tests to 
state what should be done before it is done. Whether it does always make 
sense to do that is another factor, but it is certainly an interesting 
way of looking at Unit Testing.

Another point I'd like to address is integrating specification and 
documentation. I'm doing this by embedding simple test cases into the 
documentation in the style of sample code. I can extract those and 
verify that the samples in the documentations still make sense easily.

Personally, I would also like to see a way of testing whether a given 
Object implements a contract (here: passes a suite of unit tests) -- I 
think that would be useful for multi method dispatch. (Called method 
overloading in the C++/Java world.)

Unit testing and how they can be integrated into development is a very 
interesting topic. I think they can be used for much more than they 
usually are.