Test for kv/memdb/memory_mutation.go are needed

[Giulio2002]

Memory_mutation.go contains a data structures which emulates the BTree interface of our Database, it can be thought as just a Btree which acts as a map. each mutations has tables which are set of key => value pairs like an hashmap per say, we need to tests those functions, this include IncrementSequence, GetOne, Put, ForAmount, etc.... there are some other tests written but nowhere enough for full coverage.