unit testing - Python unittest successfully asserts None is False -

why assertfalse succeed on none?

import unittest  class testnoneisfalse(unittest.testcase):     def test_none_is_false(self):         self.assertfalse(none) 

results:

> python -m unittest temp . ---------------------------------------------------------------------- ran 1 test in 0.001s  ok 

it seems if behaviour invites errors function not return value. example:

def is_lower_than_5(x):     if x < 5:         return true     elif x > 5:         return false  ....  def test_5_is_not_lower_than_5(self):    self.assertfalse(is_lower_than_5(5)) 

the above test pass though should fail. missing error in code should caught.

how should assert value literally false , not merely false in boolean context? e.g.

self.assertequals(false, none)  # assert fails. good! 

none falsy, 0, "", [], ...

assertfalse not check whether given value false identity. behavior consistent if statement:

if not none:     print('falsy value!') 

similarly, asserttrue not check whether value true, , such values 1, "abc", [1, 2, 3] pass test. see truth value testing more information.

this behavior explicitly documented:

asserttrue(expr, msg=none) assertfalse(expr, msg=none)

test expr true (or false).

note equivalent bool(expr) true , not expr true

if want sure value true or false, use assertis.