Any test you write without the knowledge of internals is good only to tell you that this particular test failed, and says nothing on the sanity of the microcontroller as a whole. The microcontroller might be well out of operational order and still execute a particular set of tests OK, notabene if the "result shall be a single number".

Just a trivial (and unrealistic, but you got the idea) example: if the accumulator is the first thing to fail and if it fails so that it returns all zeros no matter what is written to it; and if the last operation of the test is anl a,something, and you'd expect it to return zero based on previous operations on "something", the test will pass no matter what.

JW