I get a weird linker error, whenever a unit test covers code that contains PX4_INFO / ERROR / WARNING statements or makes use of the timing functionality.
As an example: I add a PX4_INFO("foo");
and the corresponding #include <px4_log.h>
somewhere in the Attitude Control and then try to make tests TESTFILTER=Attitude
results in a linker error, but make px4_fmu-v5_default
compiles just fine.