Some tests doesn't need call bitbake so it is better to use the
basic unittest case class.
[YOCTO #10828]
(From OE-Core rev: 4d01610f36eaee8da3126bb5045856279371fd17)
Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>