It's the first test where more than one memory cell needs to be modified.

Do I miss something in the problem statement?

E.g. is this test correct?

azkazkazkazkazkazkazoazv

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++.+++++++++++++++++++++++++.<+++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++.>>+++++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++.<.<.>>.<.<.>>.<.<.>>.<.<.>>.<.<.>>.<.<++++.>>.<.----.

Try this test:
azqhazqhazqhazqhazqhazqhazqhazqhazqhazqhazqhazqh

My answer:
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++.+++++++++++++++++++++++++.<+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++.<++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++.<+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++.>>>.<.<.<.>>>.<.<.<.>>>.<.<.<.>>>.<.<.<.>>>.<.<.<.>>>.<.<.<.>>>.<.<.<.>>>.<.<.<.>>>.<.<.<.>>>.<.<.<.>>>.<.<.