方法1：
修改AndroidManifest.xml 中android:testOnly="true" 改成 android:testOnly="false"，或者直接去掉。
方法2：
adb push *.apk /tmp
adb shell pm install -t /tmp/*.apk
方法3：
adb install -t *.apk 方法4：
Android Studio 3.0 and FLAG_TEST_ONLY 一文中，给出了关于Android studio 3.0中出现问题的说明：
Option to indicate this application is only for testing purposes.
For example, it may expose functionality or data outside of itself that would cause a security hole, but is useful for testing.
This kind of application can not be installed without the INSTALL_ALLOW_TEST flag, which means only through adb install.
1. You cannot install an app with android:testOnly="true" by conventional means, such as from an Android file manager or from a download off of a Web site
2. Android Studio 3.0 sets android:testOnly="true" on APKs that are run from the IDE
解决办法： 在gradle.properties(项目根目录或者gradle全局配置目录 ~/.gradle/)文件中添加： android.injected.testOnly=false
