Changes in 1.2.5 appear to have made the testValueList non-functional when a validator.OneOf field is in a Schema:

class foo(Schema):
    bar = validators.OneOf((1,2,3), testValueList=True)

foo.to_python({'bar':(1,2,3)})

Result: Invalid: bar: Please provide only one value

If I add accept_iterator=True to validators.OneOf, the result is {'bar': (1, 2, 3)}