AS 3.0 INSTALL_FAILED_TEST_ONLY真正原因

首先给出正解：

其他网友的回答：

http://blog.sina.com.cn/s/blog_6cbd24890102x0ki.html

关键部分内容复制一下：

Note: The Run button builds an APK with testOnly="true", which means the APK can only be installed  via adb (which Android Studio uses). If you want a debuggable APK that people can install without adb,  select your debug variant and click Build > Build APK(s).
也就是说，只要在AndroidStudio3.0内，点击绿三角运行Run，跑出来的apk，一定是TEST_ONLY的。