add a test case indicating we reset the stats when starting a new fragme...

...nt

Don't merge. Also bypass the bug of ENG-6517 by using inequality checking instead of equality checking.

Still need to discuss on the test case which indicates the peak memory usage is larger than the "current" memory usage.
It doesn't matter for the test, but it's a little confusing that warehouse_half is not referenced here. It would be better just to drop  warehouse and reference warehouse_half here.