refactor AbstractFsRiverTest and format code using intellij to fix the inconsistency with tabs and spaces

# Done
* I extracted some block of code from `setUpBeforeClass` and `setUp` to make these methods smaller
* I reformatted the code using IntelliJ to fix the inconsistency between spaces and tabs. I picked tabs.
* I move default values for `mapping()` and `waitingTime()` to the superclass to avoid duplication.

# Next move
* Make tests deterministic