Write unit tests for KeyValueStore & PropertiesKeyValueStore

[wurmf]

[wurmf]

In order to do tests against the KeyValueStore interface it is a good idea to do the instantiation through the spring dependency injection. If the instantiation is done through the spring framework, then there must be a TestStorageHandler in the test package, which creates the openbooth home directory inside a temporary folder so it does not change anything inside the production environment.

[wurmf]

This might also be necessary for other tests, which persist values or store files.

[wurmf]

For code reuse it would be a good idea to use the StorageHandler implementation, but with a changed storage path. To do so it is necessary to let the TestStorageHandler extend the StorageHandler implementation and let the StorageHandler implementation store the storage path in a protected variable, which can be accessed and changed by the constructor of the TestStorageHandler.

[wurmf]

The TestStorageHandler now has a seperate issue #66