Re: [Mockobjects-java-users] Mock object tests expose class implementation details

[Steve F. <st...@m3...>]

> From: "Martin Bayly" <mar...@ho...>
> I've been using mock objects on a new project for the last few weeks
and I really like
> the level of isolation I can achieve between the class being tested
and other domain
> code on which the class depends.  They make tests simpler to setup and
easier/faster
> to run.  I'm developing in a servlet/ejb environment and I've got
useful implementations
> of mock session and entity beans going which allow me to test a lot of
container
> dependent code without the container.

> However, one thing that concerns me is that my tests seem to expose
the implementations
> of the classes being tested.  I really like the XP practice of test
first by intention (code
> what you want not how to do it).  However, when writing my mock object
based tests
> I'm generally thinking about the implementation as I write the test,
as the expectations that
> I want to set and verify depend on what I'm expecting the code to do
internally.
> Without mock objects I tend to be more focused on externally
verifiable consequences
> of calling a method (which seem to be more intention based).

> I'm concerned this might make future refactoring more difficult
because refactoring may
> require me to change the expectations and verifications.  Hopefully,
this won't be the
> case because generally I'm using mock objects for other higher level
objects such as
> other ejbs or framework classes which should have well defined
interfaces that won't change much.

> Also maybe I'm not exposing implementation.  I'm just making it easy
to verify things that
> I would otherwise have to verify externally, but which might be
difficult to setup in a unit
> test environment.  e.g. if a method being tested creates a new entity
bean as part of its
> implementation, without mock objects, I would have to make some call
as part of the test
> to verify the entity was actually created.  With mock objects I just
verify that my method called my mock entity bean's create() method with
the right parameters.  Much simpler, faster and no database
dependencies.

I was wondering if anyone else had any comments on the impact of mock
objects on the test first by intention practice.  Sorry for rambling!

Regards,

Martin Bayly
mar...@ho...