Unittest (sometimes) fails because floating-point imprecision

Question

I have a class Vector that represents a point in 3-dimensional space. This vector has a method normalize(self, length = 1) which scales the vector down/up

Answer 1

I suppose one possibility is to apply the function to test cases for which all inputs, the results of all intermediate calculations, and the output are exactly representable by float.

To illustrate:

In [2]: import math

In [4]: def norm(x, y):
   ...:     return math.sqrt(x*x + y*y)
   ...: 

In [6]: norm(3, 4) == 5
Out[6]: True

Not sure how practical this is though...