在使用 Google App Engine 1.8.8 为我们的应用程序编写单元测试时，我们使用LocalServiceTestHelper，在使用setUp()注释的方法中调用@Before，以及tearDown()注释的方法中的@After。
偶尔（但并非总是如此），调用tearDown()似乎会引发ClassCastException并没有太多解释。
java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.io.ObjectStreamClass
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1511)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1771)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
at java.util.ArrayList.readObject(ArrayList.java:771)
at sun.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1017)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1893)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1990)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1915)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
at java.util.HashMap.readObject(HashMap.java:1184)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1017)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1893)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1990)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1915)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
at java.util.HashMap.readObject(HashMap.java:1184)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1017)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1893)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1990)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1915)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1990)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1915)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
at java.util.HashMap.readObject(HashMap.java:1184)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1017)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1893)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1990)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1915)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1798)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
at com.google.appengine.api.datastore.dev.LocalDatastoreService.load(LocalDatastoreService.java:1620)
at com.google.appengine.api.datastore.dev.LocalDatastoreService.startInternal(LocalDatastoreService.java:563)
at com.google.appengine.api.datastore.dev.LocalDatastoreService.access$300(LocalDatastoreService.java:137)
at com.google.appengine.api.datastore.dev.LocalDatastoreService$2.run(LocalDatastoreService.java:556)
at java.security.AccessController.doPrivileged(Native Method)
at com.google.appengine.api.datastore.dev.LocalDatastoreService.start(LocalDatastoreService.java:553)
at com.google.appengine.tools.development.ApiProxyLocalImpl.startServices(ApiProxyLocalImpl.java:599)
at com.google.appengine.tools.development.ApiProxyLocalImpl.access$700(ApiProxyLocalImpl.java:46)
at com.google.appengine.tools.development.ApiProxyLocalImpl$2.run(ApiProxyLocalImpl.java:584)
at com.google.appengine.tools.development.ApiProxyLocalImpl$2.run(ApiProxyLocalImpl.java:581)
at java.security.AccessController.doPrivileged(Native Method)
at com.google.appengine.tools.development.ApiProxyLocalImpl.getService(ApiProxyLocalImpl.java:580)
at com.google.appengine.tools.development.testing.LocalServiceTestHelper.getLocalService(LocalServiceTestHelper.java:519)
at com.google.appengine.tools.development.testing.LocalDatastoreServiceTestConfig.getLocalDatastoreService(LocalDatastoreServiceTestConfig.java:294)
at com.google.appengine.tools.development.testing.LocalDatastoreServiceTestConfig.tearDown(LocalDatastoreServiceTestConfig.java:288)
at com.google.appengine.tools.development.testing.LocalServiceTestHelper.tearDown(LocalServiceTestHelper.java:462)
at com.myapplication.TestClass.teardown(TestClass.java:107)
有没有其他人偶然发现这个问题，并设法解决了这个问题？我在NullPointerException calling tearDown() on Google App Engine LocalSErviceTestHelper发现了类似的问题，但我已经确认我的 GAE 版本都无法使用。