Make `src/Classic/Solvers/GreenWakeFunction::testApply()` a unit test
The following discussion from !269 (merged) should be addressed:
@snuverink_j started a discussion:
It should be made into a unit test. I will open a new issue for it.
The preprocesser definition
#ifdef ENABLE_WAKE_TESTS and the function
src/Classic/Solvers/GreenWakeFunction.cpp should be transformed into a unit test.