We need 2 kinds of tests:

1. For storage components (blobstor, metabase, writecache, pilorama, shard as a whole):

   1. All operations are idempodent, i.e. SetMode, Close, Open do not panic if called twice and do nothing on the second call.
   2. Check all possible mode transitions (SetMode between all pair op modes, the latest SetMode should be checked for correctness, Open in RW/RO mode, following some SetMode).
   3. Maybe, some fuzzing can help here: generate random byte array, each byte decodes and operation on a specific component, check that no panic occurs.

2. After Unify blobstor interfaces #1584, we can write test suite for the blobstor component interface and reuse it for testing fstree, blobovnicza trees and any future blobstor components.