how HSQL work in examples!

hello there,
I find the code below in JDBCExample
```java
conn = DriverManager.getConnection("jdbc:hsqldb:db_file", "sa", "");
```

and I can't run the UnitTests for db connect failed, I found the website of HSQL, there are three type of the HSQL db, like "jdbc:hsqldb:file: xxx" or "jdbc:hsqldb:mem:xxx",but no use in the examples, so I wonder how HSQL here works!