brew postinstall mysql

$ mysql -u root -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 10
Server version: 8.0.13 Homebrew

Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY '';

mysql -e 'CREATE DATABASE mysqltest;' -uroot
mysql -e 'GRANT ALL PRIVILEGES ON mysqltest.* TO root@localhost WITH GRANT OPTION' -uroot

brew services start mysql
brew services stop mysql