unittest: Proposal to add failUnlessNear

Antoon Pardon apardon at forel.vub.ac.be
Tue Jul 20 09:59:01 CEST 2004

Op 2004-07-19, John Roth schreef <newsgroups at jhrothjr.com>:
> "Antoon Pardon" <apardon at forel.vub.ac.be> wrote in message
> news:slrncfnaq7.kj.apardon at trout.vub.ac.be...
>> I have been working with unittests lately and found that the
>> self.failUnlessAlmostEqual, isn't as usefull as it could be.
>> My main problem is, that it is only usefull with objects
>> that can be converted to floats, while there are a whole
>> bunch of objects that can be almost equal but not so
>> convertable. The first example coming to mind being
>> complex numbers.
>> A secondary objection is that you are limited to
>> a very specific set of tolerances. If for instance
>> you want to verify that two numbers differ at most
>> by 0.0003 you can't specify that.
> Float and complex have two very different issues.

Only if you want them to be. Floats are a subset
of complex and as such can be treated exactly
the same.

> Since I'm maintaining the Python port of FIT, I
> had to deal with them. What I did for float was
> use the character form of the float to determine
> the precision. The default routine appends a
> character 5 and then uses this to calculate the
> bounds within which the other value must be found.
> An example may help. Let's say I want to
> test against '6.23e14'. This method would
> establish bounds of 6.235e14 and 6.225e14
> and then test whether the other number was
> within those bounds. (Note that the '5' is
> appended before the numbers are converted
> to float, however the second bound is calculated
> after the conversion.)

Why don't you just test whether the second
number lies within a fault tolerance of
5e11 of 6.23e14

> There's also a way of prescribing something other
> than '5' to append. This approach is due to
> Ward Cunningham; what I did was move it
> from the ScientificDouble class to the base
> float type adapter. (The Java source can be
> located in a number of places, including
> fit.c2.com and www.fitnesse.org. The Python
> source is in the files section of the Extremeprogramming
> and fitnesse Yahoo groups. You're welcome
> to copy the approach, but since Ward put it
> under the GPL, I don't think it can be directly
> dropped into unittest.)
> Complex, on the other hand, should be dealt
> with by calculating the distance between the
> two values in the i,j plane
> and then seeing if this distance is within a given
> bound. The bound should, of course, be a
> separately specifiable parameter.

There is no reason floats should be treated differently.
If you want to, be my guest, but there really is no
need, and doing so when you are working with both
just complicates things needlessly.

> One major issue is that these are very type specific;
> the methods should be called something like
> "failUnlessFloatWithinTolerance" and
> "failUnlessComplexWithinTolerance".

Why? calculating the distance between numbers and
checking whether this distance is within bounds
works just as good for floats as it does for
complex numbers. We don't need an absForFloat
and an absForComplex either. So why do you want
to split this up?

Antoon Pardon

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