IWYU cleanup
Add tests for DDL generation
Add tests for DDL extension
Add cleanup steps to various tests

To avoid leaving cruft between tests.
Add AppendShardIdToName tests
Cleanup
Shard creation testing

Phew.
Add shard pruning tests
Add repair_shard tests; fix bug

Next up: integration testing.
Header fixes
Add modification tests
Add tests for SELECT queries
Add utility tests