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.
Breaking out the different test functions is good. It is helpful when analyzing why tests fail and saves time when you want to debug one test case at a time. 
But please shrink this file by doing some refactoring the common code used by these different test functions into one or more "prepare" functions -- if you need to "return" more than one result value from a shared "prepare" function, it is OK to change a local variable into a data member so it can be set in the "prepare" function and used in different test functions. Use the "m_" prefix data member naming convention for these and declare them as private at the top of the class before any methods.