艾玛失败了，如何调试在模拟器上运行的android测试用例？

Question

我试图通过在我的 mavenized android 项目上运行 ant emma 来获取覆盖率报告，其他一切都很顺利，但是当运行

ant emma debug install test. 

输出时我遇到了 NullPointerException：

test:
 [echo] WARNING: Code Coverage is currently only supported on the emulator and rooted devices.
 [echo] Running tests ...
 [exec] 
 [exec] com.jayway.maven.plugins.android.generation2.samples.libraryprojects.mainapp.MainActivityTest:INSTRUMENTATION_RESULT: shortMsg=java.lang.NullPointerException
 [exec] INSTRUMENTATION_RESULT: longMsg=java.lang.NullPointerException: Unable to start activity ComponentInfo{com.jayway.maven.plugins.android.generation2.samples.libraryprojects.mainapp/com.jayway.maven.plugins.android.generation2.samples.libraryprojects.mainapp.MainActivity}: java.lang.NullPointerException
 [exec] INSTRUMENTATION_CODE: 0
 [echo] Downloading coverage file into project directory...
 [exec] remote object '/data/data/com.jayway.maven.plugins.android.generation2.samples.libraryprojects.mainapp/coverage.ec' does not exist

如何调试这个？我想知道NPE发生在哪里。