Previously installed certificate is invalid, and download the certificate must be copied to / system / etc / security / cacerts / directory,
DETAILED DESCRIPTION OF THE reference the following article.
https://blog.csdn.net/ShadowySpirits/article/details/79756274
如果遇到 remount of the / superblock failed: Permission denied
Solution https://blog.csdn.net/afei__/article/details/83058933 .
redmi k20, Android version 9.0, effective pro-test.