Comment 7 for bug 533015

@Nikolay: thx for the extra tests

I committed a modified version of that as:

# the object still fits into the cache, so it should be there
self.assert_(cache.total_estimated_size >= 100)

but retained the old test for <= 1000. Depending on the platform the value was apparently either 0 or "-1" expressed at 2**32, so we need to test both conditions.