For floating points it would be good to also have something related to unit of least precision like I think it exists in google tests:

assert: aFloat isWithin: anInteger ulpFrom: anotherFloat

������ ^(aFloat - anotherFloat) abs <= (anotherFloat ulp max: aFloat ulp)

It's testing if the result are the same with a tolerance on least significant bits.
(anotherFloat ulp max: aFloat ulp) is not really necessary, it's only for making the comparison symmetric.

indeed, 2 and 2 predecessor do not have the same exponent, so do not have the same ulp.

If we don't have symmetry, then

������ self assert: 2.0 predecessor predecessor isWithin: 1 ulpFrom: 2.0.
might differ from:
������ self assert: 2.0 isWithin: 1 ulpFrom: 2.0 predecessor predecessor .

Note that the this message cannot be used to test for zero result (because 0.0 ulp is the smallest denormal).

For example:

������ self assert: 2.0 - 2.0 predecessor isWithin: 4 ulpFrom: 0.0.

would anwer false, but it makes no sense!

One should write

������ self assert: 2.0 isWithin: 4 ulpFrom: 2.0 predecessor.