1) Configure dash to be default shell (/bin/sh -> bash);
2) Enable ptest using: DISTRO_FEATURES_append = " ptest";
3) Build a recipe that contains a ptest package (ex strace);
4) Look in the log.do_configure_ptest_base or log.do_compile_ptest_base
and you will find the following error:

108: [: a-t:: unexpected operator

The problem comes from the ptest.bbclass where "type -t" is used to determine if the ptest functions are defined(lines 21,29,42). In dash "type" does not accept -t as a parameter.