You can run tests in MySQL in memory almost as easily.

   database-autotests:
       volumes:
          - mysql-autotests-volume:/var/lib/mysql

   volumes:
       mysql-autotests-volume:
       driver_opts:
       type: tmpfs
       o: "size=2G,mode=777"
       device: tmpfs

It's also very fast and allows to test the code on the same database, especially if you have something MySQL-specific.