Example error:

______________ TestOpenParticipantsRegistration.test_contest_info ______________

self = <oioioi.participants.tests.TestOpenParticipantsRegistration testMethod=test_contest_info>

    def test_contest_info(self):
        contest = Contest.objects.get()
        user = User.objects.get(username='test_user')
        p = Participant(contest=contest, user=user)
        p.save()
> OpenRegistration(participant_id=p.id, **self.reg_data).save()

oioioi/participants/tests.py:252:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
../virtualenv/lib/python2.7/site-packages/django/db/models/base.py:796: in save
    force_update=force_update, update_fields=update_fields)
../virtualenv/lib/python2.7/site-packages/django/db/models/base.py:824: in save_base
    updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
../virtualenv/lib/python2.7/site-packages/django/db/models/base.py:908: in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
../virtualenv/lib/python2.7/site-packages/django/db/models/base.py:947: in _do_insert
    using=using, raw=raw)
../virtualenv/lib/python2.7/site-packages/django/db/models/manager.py:85: in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
../virtualenv/lib/python2.7/site-packages/django/db/models/query.py:1045: in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
../virtualenv/lib/python2.7/site-packages/django/db/models/sql/compiler.py:1053: in execute_sql
    for sql, params in self.as_sql():
../virtualenv/lib/python2.7/site-packages/django/db/models/sql/compiler.py:1006: in as_sql
    for obj in self.query.objs
../virtualenv/lib/python2.7/site-packages/django/db/models/sql/compiler.py:945: in prepare_value
    value = field.get_db_prep_save(value, connection=self.connection)
../virtualenv/lib/python2.7/site-packages/django/db/models/fields/__init__.py:755: in get_db_prep_save
    prepared=False)
../virtualenv/lib/python2.7/site-packages/django/db/models/fields/__init__.py:747: in get_db_prep_value
    value = self.get_prep_value(value)
../virtualenv/lib/python2.7/site-packages/django/db/models/fields/__init__.py:1025: in get_prep_value
    return self.to_python(value)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <django.db.models.fields.BooleanField: terms_accepted>, value = 'y'

    def to_python(self, value):
        if value in (True, False):
            # if value is 1 or 0 than it's equal to True or False, but we want
            # to return a true bool for semantic reasons.
            return bool(value)
        if value in ('t', 'True', '1'):
            return True
        if value in ('f', 'False', '0'):
            return False
        raise exceptions.ValidationError(
            self.error_messages['invalid'],
            code='invalid',
> params={'value': value},
        )
E ValidationError: [u"'y' value must be either True or False."]

../virtualenv/lib/python2.7/site-packages/django/db/models/fields/__init__.py:1018: ValidationError