tst_Parser: update the validation test

There were a couple of mistakes in the test names ("bytearray" while
testing negative numbers and "string" while testing byte arrays) and
there were gaps in the testing.

This also removes the highly unnecessary offset testing, since it's
fragile and changes often with the code updates.

Signed-off-by: Thiago Macieira <[email protected]>

Author: thiagomacieira