Hi Peter
The internal ram test is part of the BIT, as you said all other parts of the 8052 has been tested, I only found difficulty in ram test for the reasons we were discussing above.
The BIT is to verify that the 8052 is working properly and has nothing to do with manufacturers tests. the chip might fail anytime due to various reasons. so if you are designing sensitive application you want to make sure that your chip is working properly before you rely on its decisions.
thanx
Mahmood