In #9633, we've spotted a bad fp-comparison in naive_bayes.py
In naive_bayes.py, we have

if priors.sum() != 1.0:
    raise ValueError('The sum of the priors should be 1.')

which sometimes fails unexpectedly.

import numpy as np
priors = np.array([0.08, 0.14, 0.03, 0.16, 0.11, 0.16, 0.07, 0.14, 0.11, 0.0])
my_sum = np.sum(priors)
print('my_sum: ', my_sum)
print('naive: ', my_sum == 1.0)
print('safe: ', np.isclose(my_sum, 1.0))

#('my_sum: ', 1.0000000000000002)
#('naive: ', False)
#('safe: ', True)

The problem is solved in GaussianNB for 'priors' (See #10005), but that's far from enough, we have similar problems, e.g., in discriminant_analysis.py:

So the problem here is:
(1) Figure out a way to detect similar issues in the repo
(2) Fix these issues (honestly I don't think we need a test for these issues)