Open boundaries are more difficult to test, but there are ways to approach them.
Actually the best solution to the problem is to find out what the boundary should be
specified as! One approach is to go back to the specification to see if a maximum
has been stated somewhere else for a balance amount. If so, then we know what our
boundary value is. Another approach might be to investigate other related areas of
the system. For example, the field that holds the account balance figure may be only
six figures plus two decimal figures. This would give a maximum account balance
of $999 999.99 so we could use that as our maximum boundary value. If we really
cannot find anything about what this boundary should be, then we probably need to
use an intuitive or experience-based approach to probe various large values trying to
make it fail.
We could also try to find out about the lower open boundary
– what is the lowest
negative balance? Although we have omitted this from our example, setting it out
in the table shows that we have omitted it, so helps us be more thorough if we
wanted to be.
Representing the partitions and boundaries in a table such as this also makes it
easier to see whether or not you have tested each one (if that is your objective).
Extending equivalence partitioning and boundary value analysis
So far, by using EP and BVA we have identified conditions that could be tested,
i.e. partitions and boundary values. The techniques are used to identify test conditions,
which could be at a fairly high level (e.g.
‘low-interest account’) or at a detailed
level (e.g.
‘value of $100.00’). We have been looking at applying these techniques to
ranges of numbers. However, we can also apply the techniques to other things.
For example, if you are booking a flight, you have a choice of Economy/Coach,
Premium Economy, Business or First Class tickets. Each of these is an equivalence
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