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It is true
that in
order to
test any
system
effectively,
we need to
first
understand
what the
implementation
under test
is supposed
to do. With
continuously
increasing
complex
software,
testers can
use models
to
understand
the system
and support
test design
process. |
Dr. Kaner has rightly
suggested that testing is a
technical investigation;
this view is similar to the
observation mage by Binder
(2000) in ‘Testing Object
Oriented Systems’ where he
looks at the testing as a
search problem. In the vast
amount of input, we are
looking for just few inputs
which will trigger the
defect or faulty behaviour
of the system. According to
the model based testing
approach, this search should
be systematic, focused and
automated.
In Model Based Testing,
input and state combination
can be enumerated
systematically. In order to
understand the model, it is
important to understand the
concept behind model first.
According to Binder (2000),
every model has four main
elements: subject, point of
view/theory, representation
and technique.
-
Subject - Is the core idea around which models are
created. In testing,
typically models of
system under test help
us in selecting
effective test cases.
-
Point of View - A model must be based on the frame of
reference and principle
that can guide
identification of
relevant issues and
information. Software
testing models typically
express required
behaviour and focus
aspects of system
suspected to be buggy.
Models from the software
testing point of view,
must establish the
information necessary to
produce and evaluate
test case.
-
Representation - A modelling technique must have a means
of expressing a
particular model. This
may be a wire frame, cad
model or anything else.
-
Technique - Models can be developed by using any
technique using UML
notion for the formal
ones or even simpler
artefact for general
use.
Before dwelling in to the
skills required to perform
model based testing, let us
first understand how models
can be used in testing
complex software and what
kind of information can be
revealed from the models.
Following list summarizes
main activities that can be
done effectively with the
models
-
Model Validation & Consistency checking – Models can be
validated against the
rules defined in OCL,
Object constraint
language and meta-model.
-
Product Validation – Product can be validated using
models in more than one
way. It can be tested
that observable
behaviour of model is
appropriate and also
this observable
behaviour confirms to
the required behaviour.
One important thing that a
software tester needs to
understand is how models can
be used to improve the way
testing is done. Techniques
described above are formal
techniques and are based on
the assumption that models
of the product being
developed are in place and
our testing efforts are
derived from those models.
Even in the absence of
formal models, test team can
create their own models to
understand the problem
domain in a better way.
Bezier characterize this
(taken from Binder, 2000) in
a very neat way and says
“What shall we, as testing
practitioner do? As with all
models, we ignore the
complexities that can
invalidate the model and we
use what we can apply with
ease. After all, models for
testing are intended to give
us insight into effective
test case design – they are
intuition joggers – so it
does not matter if they are
imperfect as long as the
resulting tests are good. ” |
