getInstrumentation（）。getTargetContext（）返回一种android.app.Context类型。但我觉得它是android.app.ApplicationContext的基类，因为我在以下日志中得到了类强制转换异常。
和
getActivity（）。getApplicationContext（）返回一种android.app.Context类型，尽管它实际上返回了我的ActivityInstrumentationTestCase2实现定义的活动的基类。
logcat的：
04-04 21:02:27.036: INFO/TestRunner(431): started: testIt(edu.rockies.rockies.activity.courses.test.TopicTest)
04-04 21:02:27.126: INFO/TestRunner(431): failed: testIt(edu.rockies.rockies.activity.courses.test.TopicTest)
04-04 21:02:27.126: INFO/TestRunner(431): ----- begin exception -----
04-04 21:02:27.136: INFO/TestRunner(431): java.lang.ClassCastException: android.app.ApplicationContext
04-04 21:02:27.136: INFO/TestRunner(431): at edu.rockies.rockies.activity.courses.test.TopicTest.setUp(TopicTest.java:27)
04-04 21:02:27.136: INFO/TestRunner(431): at junit.framework.TestCase.runBare(TestCase.java:125)
04-04 21:02:27.136: INFO/TestRunner(431): at junit.framework.TestResult$1.protect(TestResult.java:106)
04-04 21:02:27.136: INFO/TestRunner(431): at junit.framework.TestResult.runProtected(TestResult.java:124)
04-04 21:02:27.136: INFO/TestRunner(431): at junit.framework.TestResult.run(TestResult.java:109)
04-04 21:02:27.136: INFO/TestRunner(431): at junit.framework.TestCase.run(TestCase.java:118)
04-04 21:02:27.136: INFO/TestRunner(431): at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:169)
04-04 21:02:27.136: INFO/TestRunner(431): at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:154)
04-04 21:02:27.136: INFO/TestRunner(431): at android.test.InstrumentationTestRunner.onStart(InstrumentationTestRunner.java:430)
04-04 21:02:27.136: INFO/TestRunner(431): at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1447)
04-04 21:02:27.136: INFO/TestRunner(431): ----- end exception -----
04-04 21:02:27.156: INFO/TestRunner(431): finished: testIt(edu.rockies.rockies.activity.courses.test.TopicTest)