H2 database is an embedded database that widely used in testing, local storage and caching.
The H2 database installation contains a web based database client, in which you can create database, table, insert data and query data.
H2 is an embedded database written with Java. The database will be loaded in to application as a class library.
Testing database related functionalities needs preparing and cleaning data in database. Most database will persistent data to disk, and they usually takes time to start up and shut down.