在 models.py 中给出以下代码：

  class Member（ndb.Model）：

 name = ndb.StringProperty（）

 $ b def remove_duplicates（prop，value）： 
举例Exception（'Duplicate'）


 class Club1（ndb.Model）：

 members = ndb.StructuredProperty（Member，repeated = True ，validator = remove_duplicates）
 

我可以创建一个 Member instance

> m = Member（name ='Alice'）

创建一个 Club1 这个成员实例会触发验证：

 > c1 = models.Club1（members = [m]）
 Traceback（最近一次调用最后一次）：
< snip> 
文件models.py，第60行，在remove_duplicates中
举例异常（'重复'）
异常：重复
 $ p $然而，创建一个空的 Club1 实例，然后附加一个 Member  >不会：这实际上是您的测试用例。
 > c1 = models.Club1（）
> c1.members.append（m）
> c1.put（）
 Key（'Club1'，6682831673622528）
 
 code> ndb.StructuredProperty 并将验证放在子类中： 

  class MembersStructuredProperty ndb.StructuredProperty）：
 $ b $ def _validate（self，value）：
异常（'重复'）


类Club2（ndb.Model ）：

 members = MembersStructuredProperty（Member，repeated = True）
 
创建一个 Club2 实例与一个 Member 会像之前一样触发验证：
 &GT; c2 = models.Club2（members = [m]）
 Traceback（最近的最后一次调用）：
< snip> 
在_validate 
中引用models.py，第56行，引发异常（'重复'）
例外：重复
 
现在如此追加一个 Member ，然后尝试写入数据存储区：
 > c2 = models.Club2（）
> c2.members.append（m）
> c2.put（）
 Traceback（最近一次调用最后一次）：
< snip> 
在_validate 
中引用models.py，第56行，引发异常（'重复'）
例外：重复
 
因此，子类化 ndb.StructuredProperty 应该允许您的测试通过。
 

 我不知道为什么ndb的属性验证行为如此，可以说这是一个错误，或者至少是没有记录的行为。
     strong>编辑：  

正如@DanCornilescu在评论中指出的，这是 SDK中的已知错误 
 
Here is my ndb Model 
from google.appengine.ext import ndb
from mainsite.rainbow.models.CFCSocialUser import CFCSocialUser


class CFCSocialGroup(ndb.Model):

    def remove_duplicate(self, value):
        raise Exception("Duplicate user detected")

    name = ndb.StringProperty(required=True)
    created_on = ndb.DateTimeProperty(auto_now_add=True)
    updated_on = ndb.DateTimeProperty(auto_now=True)
    created_by = ndb.StructuredProperty(CFCSocialUser)
    members = ndb.StructuredProperty(CFCSocialUser, repeated=True, validator=remove_duplicate)

    @staticmethod
    def create_group(name):
        """Create a new group"""
        group = CFCSocialGroup(name=name)
        return group

    def add_member(self, social_user):
        """Add a member to the local group"""
        self.members.append(social_user)
I am trying to ensure that I do not add the same user to a given group. So I trying to validate the value of members property (StructuredProperty). 

My tests is
from unittest import TestCase
from mainsite.rainbow.models.CFCSocialGroup import CFCSocialGroup
from tests.test_CFCSocialUser import create_user
from tests.cfcsocialtests.testbase import CFCTestBase_NDB
from nose.tools import *
from nose.plugins.attrib import attr


class TestCFCSocialGroup(CFCTestBase_NDB):
    @attr("CRUD")
    @raises(Exception)
    def test_duplicate_addition(self):
        """Test to detect duplicate users in groups"""
        user1 = create_user()
        user2 = create_user()
        group = CFCSocialGroup.create_group('Group1')
        group.add_member(user1)
        group.add_member(user2)
The test fails to raise an exception. 

Here is the debug code
    FAILED (errors=1)
MacBook-Pro:tests vinay$ nosetests -v test_CFCSocialGroup.py
Test to detect duplicate users in groups ... FAIL

======================================================================
FAIL: Test to detect duplicate users in groups
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Library/Python/2.7/site-packages/nose/tools/nontrivial.py", line 67, in newfunc
    raise AssertionError(message)
AssertionError: test_duplicate_addition() did not raise Exception
-------------------- >> begin captured logging << --------------------
root: DEBUG: Using threading.local
root: WARNING: No ssl package found. urlfetch will not be able to validate SSL certificates.
root: DEBUG: all_pending: add <Future 10d0d2e90 created by _put_async(model.py:3467) for tasklet put(context.py:787); pending>
root: DEBUG: nowevent: _help_tasklet_along
root: DEBUG: Sending None to initial generator put(context.py:787)
root: DEBUG: all_pending: add <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_set_tasklet).add(('NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw', 0), ('set', 32, '', None)); pending>
root: DEBUG: AutoBatcher(_memcache_set_tasklet): creating new queue for ('set', 32, '', None)
root: DEBUG: initial generator put(context.py:787) yielded <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_set_tasklet).add(('NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw', 0), ('set', 32, '', None)); pending>
root: DEBUG: <Future 10d0d2e90 created by _put_async(model.py:3467) for tasklet put(context.py:787) suspended generator put(context.py:810); pending> is now blocked waiting for <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_set_tasklet).add(('NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw', 0), ('set', 32, '', None)); pending>
root: DEBUG: idler: _on_idle
root: DEBUG: AutoBatcher(_memcache_set_tasklet): 1 items
root: DEBUG: all_pending: add <Future 10d0ec250 created by run_queue(context.py:185) for tasklet _memcache_set_tasklet(context.py:1111); pending>
root: DEBUG: nowevent: _help_tasklet_along
root: DEBUG: Sending None to initial generator _memcache_set_tasklet(context.py:1111)
root: DEBUG: initial generator _memcache_set_tasklet(context.py:1111) yielded <google.appengine.api.apiproxy_stub_map.UserRPC object at 0x10d0ec490>
root: DEBUG: idler: _on_idle
root: DEBUG: idler _on_idle removed
root: DEBUG: rpc: memcache.Set
root: DEBUG: Sending {'NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw': 1} to suspended generator _memcache_set_tasklet(context.py:1122)
root: DEBUG: all_pending: success: remove <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_set_tasklet).add(('NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw', 0), ('set', 32, '', None)); result True>
root: DEBUG: suspended generator _memcache_set_tasklet(context.py:1122) returned None
root: DEBUG: all_pending: success: remove <Future 10d0ec250 created by run_queue(context.py:185) for tasklet _memcache_set_tasklet(context.py:1111); result None>
root: DEBUG: nowevent: _on_future_completion
root: DEBUG: <Future 10d0d2e90 created by _put_async(model.py:3467) for tasklet put(context.py:787); pending> is no longer blocked waiting for <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_set_tasklet).add(('NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw', 0), ('set', 32, '', None)); result True>
root: DEBUG: Sending True to suspended generator put(context.py:810)
root: DEBUG: all_pending: add <Future 10d0ec510 created by add(context.py:211) for AutoBatcher(_put_tasklet).add(CFCSocialUser(key=Key('CFCSocialUser', 'Vinay Joseph'), date_of_birth=datetime.date(1900, 3, 2), email='vinay@vinayjoseph.com', username='Vinay Joseph'), None); pending>
root: DEBUG: AutoBatcher(_put_tasklet): creating new queue for None
root: DEBUG: suspended generator put(context.py:810) yielded <Future 10d0ec510 created by add(context.py:211) for AutoBatcher(_put_tasklet).add(CFCSocialUser(key=Key('CFCSocialUser', 'Vinay Joseph'), date_of_birth=datetime.date(1900, 3, 2), email='vinay@vinayjoseph.com', username='Vinay Joseph'), None); pending>
root: DEBUG: <Future 10d0d2e90 created by _put_async(model.py:3467) for tasklet put(context.py:787) suspended generator put(context.py:824); pending> is now blocked waiting for <Future 10d0ec510 created by add(context.py:211) for AutoBatcher(_put_tasklet).add(CFCSocialUser(key=Key('CFCSocialUser', 'Vinay Joseph'), date_of_birth=datetime.date(1900, 3, 2), email='vinay@vinayjoseph.com', username='Vinay Joseph'), None); pending>
root: DEBUG: nowevent: _finished_callback
root: DEBUG: idler: _on_idle
root: DEBUG: AutoBatcher(_put_tasklet): 1 items
root: DEBUG: all_pending: add <Future 10d0ec610 created by run_queue(context.py:185) for tasklet _put_tasklet(context.py:348); pending>
root: DEBUG: nowevent: _help_tasklet_along
root: DEBUG: Sending None to initial generator _put_tasklet(context.py:348)
root: DEBUG: initial generator _put_tasklet(context.py:348) yielded <google.appengine.api.apiproxy_stub_map.UserRPC object at 0x10d0ec890>
root: DEBUG: idler: _on_idle
root: DEBUG: idler _on_idle removed
root: DEBUG: rpc: datastore_v3.Put
root: DEBUG: Sending [Key('CFCSocialUser', 'Vinay Joseph')] to suspended generator _put_tasklet(context.py:358)
root: DEBUG: all_pending: success: remove <Future 10d0ec510 created by add(context.py:211) for AutoBatcher(_put_tasklet).add(CFCSocialUser(key=Key('CFCSocialUser', 'Vinay Joseph'), date_of_birth=datetime.date(1900, 3, 2), email='vinay@vinayjoseph.com', username='Vinay Joseph'), None); result Key('CFCSocialUser', 'Vinay Joseph')>
root: DEBUG: suspended generator _put_tasklet(context.py:358) returned None
root: DEBUG: all_pending: success: remove <Future 10d0ec610 created by run_queue(context.py:185) for tasklet _put_tasklet(context.py:348); result None>
root: DEBUG: nowevent: _on_future_completion
root: DEBUG: <Future 10d0d2e90 created by _put_async(model.py:3467) for tasklet put(context.py:787); pending> is no longer blocked waiting for <Future 10d0ec510 created by add(context.py:211) for AutoBatcher(_put_tasklet).add(CFCSocialUser(key=Key('CFCSocialUser', 'Vinay Joseph'), date_of_birth=datetime.date(1900, 3, 2), email='vinay@vinayjoseph.com', username='Vinay Joseph'), None); result Key('CFCSocialUser', 'Vinay Joseph')>
root: DEBUG: Sending Key('CFCSocialUser', 'Vinay Joseph') to suspended generator put(context.py:824)
root: DEBUG: all_pending: add <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_del_tasklet).add(NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw, (0, '', None)); pending>
root: DEBUG: AutoBatcher(_memcache_del_tasklet): creating new queue for (0, '', None)
root: DEBUG: suspended generator put(context.py:824) yielded <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_del_tasklet).add(NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw, (0, '', None)); pending>
root: DEBUG: <Future 10d0d2e90 created by _put_async(model.py:3467) for tasklet put(context.py:787) suspended generator put(context.py:833); pending> is now blocked waiting for <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_del_tasklet).add(NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw, (0, '', None)); pending>
root: DEBUG: nowevent: _finished_callback
root: DEBUG: idler: _on_idle
root: DEBUG: AutoBatcher(_memcache_del_tasklet): 1 items
root: DEBUG: all_pending: add <Future 10d0ec850 created by run_queue(context.py:185) for tasklet _memcache_del_tasklet(context.py:1130); pending>
root: DEBUG: nowevent: _help_tasklet_along
root: DEBUG: Sending None to initial generator _memcache_del_tasklet(context.py:1130)
root: DEBUG: initial generator _memcache_del_tasklet(context.py:1130) yielded <google.appengine.api.apiproxy_stub_map.UserRPC object at 0x10d0ec210>
root: DEBUG: idler: _on_idle
root: DEBUG: idler _on_idle removed
root: DEBUG: rpc: memcache.Delete
root: DEBUG: Sending [2] to suspended generator _memcache_del_tasklet(context.py:1141)
root: DEBUG: all_pending: success: remove <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_del_tasklet).add(NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw, (0, '', None)); result 2>
root: DEBUG: suspended generator _memcache_del_tasklet(context.py:1141) returned None
root: DEBUG: all_pending: success: remove <Future 10d0ec850 created by run_queue(context.py:185) for tasklet _memcache_del_tasklet(context.py:1130); result None>
root: DEBUG: nowevent: _on_future_completion
root: DEBUG: <Future 10d0d2e90 created by _put_async(model.py:3467) for tasklet put(context.py:787); pending> is no longer blocked waiting for <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_del_tasklet).add(NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw, (0, '', None)); result 2>
root: DEBUG: Sending 2 to suspended generator put(context.py:833)
root: DEBUG: suspended generator put(context.py:833) returned Key('CFCSocialUser', 'Vinay Joseph')
root: DEBUG: all_pending: success: remove <Future 10d0d2e90 created by _put_async(model.py:3467) for tasklet put(context.py:787); result Key('CFCSocialUser', 'Vinay Joseph')>
root: DEBUG: all_pending: add <Future 10d0ec150 created by _put_async(model.py:3467) for tasklet put(context.py:787); pending>
root: DEBUG: nowevent: _finished_callback
root: DEBUG: nowevent: _help_tasklet_along
root: DEBUG: Sending None to initial generator put(context.py:787)
root: DEBUG: all_pending: add <Future 10d0ec990 created by add(context.py:211) for AutoBatcher(_memcache_set_tasklet).add(('NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw', 0), ('set', 32, '', None)); pending>
root: DEBUG: AutoBatcher(_memcache_set_tasklet): creating new queue for ('set', 32, '', None)
root: DEBUG: initial generator put(context.py:787) yielded <Future 10d0ec990 created by add(context.py:211) for AutoBatcher(_memcache_set_tasklet).add(('NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw', 0), ('set', 32, '', None)); pending>
root: DEBUG: <Future 10d0ec150 created by _put_async(model.py:3467) for tasklet put(context.py:787) suspended generator put(context.py:810); pending> is now blocked waiting for <Future 10d0ec990 created by add(context.py:211) for AutoBatcher(_memcache_set_tasklet).add(('NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw', 0), ('set', 32, '', None)); pending>
root: DEBUG: idler: _on_idle
root: DEBUG: AutoBatcher(_memcache_set_tasklet): 1 items
root: DEBUG: all_pending: add <Future 10d0ecd10 created by run_queue(context.py:185) for tasklet _memcache_set_tasklet(context.py:1111); pending>
root: DEBUG: nowevent: _help_tasklet_along
root: DEBUG: Sending None to initial generator _memcache_set_tasklet(context.py:1111)
root: DEBUG: initial generator _memcache_set_tasklet(context.py:1111) yielded <google.appengine.api.apiproxy_stub_map.UserRPC object at 0x10d0ecf50>
root: DEBUG: idler: _on_idle
root: DEBUG: idler _on_idle removed
root: DEBUG: rpc: memcache.Set
root: DEBUG: Sending {'NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw': 1} to suspended generator _memcache_set_tasklet(context.py:1122)
root: DEBUG: all_pending: success: remove <Future 10d0ec990 created by add(context.py:211) for AutoBatcher(_memcache_set_tasklet).add(('NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw', 0), ('set', 32, '', None)); result True>
root: DEBUG: suspended generator _memcache_set_tasklet(context.py:1122) returned None
root: DEBUG: all_pending: success: remove <Future 10d0ecd10 created by run_queue(context.py:185) for tasklet _memcache_set_tasklet(context.py:1111); result None>
root: DEBUG: nowevent: _on_future_completion
root: DEBUG: <Future 10d0ec150 created by _put_async(model.py:3467) for tasklet put(context.py:787); pending> is no longer blocked waiting for <Future 10d0ec990 created by add(context.py:211) for AutoBatcher(_memcache_set_tasklet).add(('NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw', 0), ('set', 32, '', None)); result True>
root: DEBUG: Sending True to suspended generator put(context.py:810)
root: DEBUG: all_pending: add <Future 10d0ecfd0 created by add(context.py:211) for AutoBatcher(_put_tasklet).add(CFCSocialUser(key=Key('CFCSocialUser', 'Vinay Joseph'), date_of_birth=datetime.date(1900, 3, 2), email='vinay@vinayjoseph.com', username='Vinay Joseph'), None); pending>
root: DEBUG: AutoBatcher(_put_tasklet): creating new queue for None
root: DEBUG: suspended generator put(context.py:810) yielded <Future 10d0ecfd0 created by add(context.py:211) for AutoBatcher(_put_tasklet).add(CFCSocialUser(key=Key('CFCSocialUser', 'Vinay Joseph'), date_of_birth=datetime.date(1900, 3, 2), email='vinay@vinayjoseph.com', username='Vinay Joseph'), None); pending>
root: DEBUG: <Future 10d0ec150 created by _put_async(model.py:3467) for tasklet put(context.py:787) suspended generator put(context.py:824); pending> is now blocked waiting for <Future 10d0ecfd0 created by add(context.py:211) for AutoBatcher(_put_tasklet).add(CFCSocialUser(key=Key('CFCSocialUser', 'Vinay Joseph'), date_of_birth=datetime.date(1900, 3, 2), email='vinay@vinayjoseph.com', username='Vinay Joseph'), None); pending>
root: DEBUG: nowevent: _finished_callback
root: DEBUG: idler: _on_idle
root: DEBUG: AutoBatcher(_put_tasklet): 1 items
root: DEBUG: all_pending: add <Future 10d132110 created by run_queue(context.py:185) for tasklet _put_tasklet(context.py:348); pending>
root: DEBUG: nowevent: _help_tasklet_along
root: DEBUG: Sending None to initial generator _put_tasklet(context.py:348)
root: DEBUG: initial generator _put_tasklet(context.py:348) yielded <google.appengine.api.apiproxy_stub_map.UserRPC object at 0x10d132450>
root: DEBUG: idler: _on_idle
root: DEBUG: idler _on_idle removed
root: DEBUG: rpc: datastore_v3.Put
root: DEBUG: Sending [Key('CFCSocialUser', 'Vinay Joseph')] to suspended generator _put_tasklet(context.py:358)
root: DEBUG: all_pending: success: remove <Future 10d0ecfd0 created by add(context.py:211) for AutoBatcher(_put_tasklet).add(CFCSocialUser(key=Key('CFCSocialUser', 'Vinay Joseph'), date_of_birth=datetime.date(1900, 3, 2), email='vinay@vinayjoseph.com', username='Vinay Joseph'), None); result Key('CFCSocialUser', 'Vinay Joseph')>
root: DEBUG: suspended generator _put_tasklet(context.py:358) returned None
root: DEBUG: all_pending: success: remove <Future 10d132110 created by run_queue(context.py:185) for tasklet _put_tasklet(context.py:348); result None>
root: DEBUG: nowevent: _on_future_completion
root: DEBUG: <Future 10d0ec150 created by _put_async(model.py:3467) for tasklet put(context.py:787); pending> is no longer blocked waiting for <Future 10d0ecfd0 created by add(context.py:211) for AutoBatcher(_put_tasklet).add(CFCSocialUser(key=Key('CFCSocialUser', 'Vinay Joseph'), date_of_birth=datetime.date(1900, 3, 2), email='vinay@vinayjoseph.com', username='Vinay Joseph'), None); result Key('CFCSocialUser', 'Vinay Joseph')>
root: DEBUG: Sending Key('CFCSocialUser', 'Vinay Joseph') to suspended generator put(context.py:824)
root: DEBUG: all_pending: add <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_del_tasklet).add(NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw, (0, '', None)); pending>
root: DEBUG: AutoBatcher(_memcache_del_tasklet): creating new queue for (0, '', None)
root: DEBUG: suspended generator put(context.py:824) yielded <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_del_tasklet).add(NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw, (0, '', None)); pending>
root: DEBUG: <Future 10d0ec150 created by _put_async(model.py:3467) for tasklet put(context.py:787) suspended generator put(context.py:833); pending> is now blocked waiting for <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_del_tasklet).add(NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw, (0, '', None)); pending>
root: DEBUG: nowevent: _finished_callback
root: DEBUG: idler: _on_idle
root: DEBUG: AutoBatcher(_memcache_del_tasklet): 1 items
root: DEBUG: all_pending: add <Future 10d0eca10 created by run_queue(context.py:185) for tasklet _memcache_del_tasklet(context.py:1130); pending>
root: DEBUG: nowevent: _help_tasklet_along
root: DEBUG: Sending None to initial generator _memcache_del_tasklet(context.py:1130)
root: DEBUG: initial generator _memcache_del_tasklet(context.py:1130) yielded <google.appengine.api.apiproxy_stub_map.UserRPC object at 0x10d0ece10>
root: DEBUG: idler: _on_idle
root: DEBUG: idler _on_idle removed
root: DEBUG: rpc: memcache.Delete
root: DEBUG: Sending [2] to suspended generator _memcache_del_tasklet(context.py:1141)
root: DEBUG: all_pending: success: remove <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_del_tasklet).add(NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw, (0, '', None)); result 2>
root: DEBUG: suspended generator _memcache_del_tasklet(context.py:1141) returned None
root: DEBUG: all_pending: success: remove <Future 10d0eca10 created by run_queue(context.py:185) for tasklet _memcache_del_tasklet(context.py:1130); result None>
root: DEBUG: nowevent: _on_future_completion
root: DEBUG: <Future 10d0ec150 created by _put_async(model.py:3467) for tasklet put(context.py:787); pending> is no longer blocked waiting for <Future 10b0ae1d0 created by add(context.py:211) for AutoBatcher(_memcache_del_tasklet).add(NDB9:agx0ZXN0YmVkLXRlc3RyHwsSDUNGQ1NvY2lhbFVzZXIiDFZpbmF5IEpvc2VwaAw, (0, '', None)); result 2>
root: DEBUG: Sending 2 to suspended generator put(context.py:833)
root: DEBUG: suspended generator put(context.py:833) returned Key('CFCSocialUser', 'Vinay Joseph')
root: DEBUG: all_pending: success: remove <Future 10d0ec150 created by _put_async(model.py:3467) for tasklet put(context.py:787); result Key('CFCSocialUser', 'Vinay Joseph')>
--------------------- >> end captured logging << ---------------------

----------------------------------------------------------------------
Ran 1 test in 0.035s

FAILED (failures=1)

Given this code in models.py:
class Member(ndb.Model):

    name = ndb.StringProperty()


def remove_duplicates(prop, value):
    raise Exception('Duplicate')


class Club1(ndb.Model):

    members = ndb.StructuredProperty(Member, repeated=True, validator=remove_duplicates)  
I can create a Member instance

> m = Member(name='Alice')

creating a Club1 instance with this Member instance triggers the validation:
> c1 = models.Club1(members=[m])
Traceback (most recent call last):
  <snip>
  File "models.py", line 60, in remove_duplicates
    raise Exception('Duplicate')
Exception: Duplicate
However, creating an empty Club1 instance and then appending a Member does not: this is effectively your test case.
> c1 = models.Club1()
> c1.members.append(m)
> c1.put()
Key('Club1', 6682831673622528)
We can subclass ndb.StructuredProperty and put the validation in the subclass:
class MembersStructuredProperty(ndb.StructuredProperty):

    def _validate(self, value):
        raise Exception('Duplicate')


class Club2(ndb.Model):

    members = MembersStructuredProperty(Member, repeated=True)
Creating a Club2 instance with a Member triggers the validation as before:
> c2 = models.Club2(members=[m])
Traceback (most recent call last):
  <snip>
  File "models.py", line 56, in _validate
    raise Exception('Duplicate')
Exception: Duplicate
And now so does appending a Member and then trying to write to the Datastore:
> c2 = models.Club2()
> c2.members.append(m)
> c2.put()
Traceback (most recent call last):
  <snip>
  File "models.py", line 56, in _validate
    raise Exception('Duplicate')
Exception: Duplicate
So subclassing ndb.StructuredProperty should allow your test to pass.

I don't know why ndb's property validation behaves like this, arguably it's a bug, or at least undocumented behaviour.

EDIT:

As @DanCornilescu observes in the comments, this is a known bug in the SDK