测试调用类方法的python方法

我有一个非常简单的方法:

Class Team(models.Model):
    def sides(self):
      return SideNames.objects.filter(team=self)

sidenames是与team在同一个文件中定义的另一个模型,

当我试着测试的时候:

self.assertEquals(len(t.sides()), 2)

我得到以下错误:

return SideNames.objects.filter(team=self)

attributeError:“nonetype”对象没有属性“objects”

但是如果我把测试改成

self.assertEquals(len(SideNames.objects.filter(team=t)), 2)

那我就不会出错了。从测试本身调用sidenames.objects.filter和调用实际方法有什么区别?

以下是两个类的整体,供参考。

class Team(models.Model):
    """The model for a football team."""

    class Admin:
            pass

    def __unicode__(self):
            return u'%s' % self.name

    def is_player(self, player):
            """Checks to see if 'player' is a member if this team. Returns True if they are, or False otherwise."""

            try:
                    teamPlayer = TeamPlayers.objects.get(player=player, team=self)
                    return True
            except ObjectDoesNotExist:
                    return False

    def sides(self):
            """Return the side names for this team"""
            return SideNames.objects.filter(team=self)

    def updateSides(self, side_a, side_b):
            """Update the side names"""
            names = SideNames.objects.filter(team=self);

            a = SideNames.objects.get(name = names[0].name)
            a.name = side_a
            a.save()

            b = SideNames.objects.get(name = names[1].name)
            b.name = side_b
            b.save()

    name = models.CharField("Team Name", max_length=255)
    organiser = models.ForeignKey(User)

class SideNames(models.Model):
    """Holds the names of the sides for each team"""

    class Admin:
            pass

    def __unicode__(self):
            """Pretty print the SideNames object"""
            return self.name

    team = models.ForeignKey(Team)
    name = models.CharField(max_length=128)