> I do not think that the purpose of testing is a testing of object.__sizeof__. 
> Memory consumption consists of two parts -- memory for C structure (and the 
> base object implementation works for this)

Note that object.__sizeof__ does something slightly different, though:
it uses basicsize (which may or may not contain the sizeof() invocation
of the correct C structure), and it considers tp_itemsize (which may or
may not have a correct value).

> 
>> I also realize that such tests will be fragile if the the structures
>> change. This is a good thing, IMO: anybody changing the layout of some
>> object should *have* to verify that the size computation is still correct,
>> so it's good that the test breaks if the structures change.
> 
> Such tests is too fragile. They force the programmer to write unnecessary code 
> in cases when it can be done automatically.

That's not the definition of "fragile", though. What you describe is
that writing the test this way is "tedious" (утомительный); it isn't
(necessarily) "fragile" (хрупкий). I (clearly) disagree that this
approach is "too tedious".