FWIW, grepping through Lib/test reveals the following statistics:
assertFalse: 83
assertTrue: 97
failUnless: 684
assert_: 1977
Not having assertTrue/assertFalse methods in the Library Reference does
not discourage people from using them given that they show up without
any warning in help(). (Moreover, assertTrue shows up before assert_.)
I would say it should be documented. After all it would only take a two
line patch (see attached).
(I agree with OP that assertTrue is clearer than assert_ . Although I
know that '_' is only there to avoid a conflict with the assert keyword,
assert_ always stand out as different from the other TestCase methods.)