make: "cond-op-not.mk" line 29: Not empty evaluates to true.
make: "cond-op-not.mk" line 37: Not space evaluates to false.
make: "cond-op-not.mk" line 41: Not 0 evaluates to true.
make: "cond-op-not.mk" line 49: Not 1 evaluates to false.
make: "cond-op-not.mk" line 55: Not word evaluates to false.
make: "cond-op-not.mk" line 59: Malformed conditional (!)
make: Fatal errors encountered -- cannot continue
make: stopped in unit-tests
exit status 1