FAQ:
Installation failed with message Failed to finalize session : INSTALL_FAILED_TEST_ONLY: installPackageLI.
It is possible that this issue is resolved by uninstalling an existing version of the apk if it is present, and then re-installing.
WARNING: Uninstalling will remove the application data!
Do you want to uninstall the existing application?
Resolve:
check your gradle,if it`s alpha,beta...maybe this wrong.
The cause is due to gradle version set in build.gradle of the app which is alpha version
--这个我问题是由于gradle plugin, gradle tool是beta版本，版本配置不对导致的，重新配置下工程的gradle版本 ，比如我用的是AS2.3.2
gradle配置如下：
# for android studio 2.3.2
classpath 'com.android.tools.build:gradle:2.3.2'
distributionUrl=https://services.gradle.org/distributions/gradle-3.3-all.zip
# for android studio 3.0
classpath 'com.android.tools.build:gradle:3.0.0-alpha2'
distributionUrl=https://services.gradle.org/distributions/gradle-4.0-milestone-1-all.zip