from testutils import assert_raises

assert format(5, "b") == "101"

assert_raises(TypeError, format, 2, 3, _msg='format called with number')

assert format({}) == "{}"

assert_raises(TypeError, format, {}, 'b', _msg='format_spec not empty for dict')

class BadFormat:
    def __format__(self, spec):
        return 42
assert_raises(TypeError, format, BadFormat())