title: What is a good in memory database for junit test?
body: <p>We are working on junit test and want to isolate the database dependency. So we are thinking to use in-memory database to replace the mysql database. There are some in-memory databases we could use like H2 database, HSQL. 
  My question is:
  1. Can H2 or HSQL perfectly replace mysql without any hidden trouble? Because there are might be some differences in the sql syntax.
  2. I want to know if there are better choice to replace mysql database when we work on unit test? </p>