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

By using a floating point value, you accept a small possible imprecision. Therefore, your tests should test if your computed value falls in an acceptable range such as:

theoreticalValue - epsilon < normalizedValue < theoreticalValue + epsilon

where epsilon is a very small value that you define as acceptable for a variation due to floating point imprecision.