for push in 5.1 (I will inform Trudy).
Storage engines and plugins can now have unit tests to test their components; such
test must be an executable C/C++ program which name ends with '-t' and which is
obeys the mytap protocol, it must be stored in the storage engine's or plugin's
source directory (storage/<engine> or plugin/<plugin>) or any subdirectories of
this.
The top-level Makefile target "test-unit" will run all unit tests: it will scan
the engines' and plugins' directories, recursively, and execute all executable
files which name ends with '-t'."