I was experimenting with the crash recovery of server. So I simulated a crash in dropdb command.
After the crash recovery the server seems to be in inconsistent state. The pg_database still has the dropped database's information. But when I try to connect to that DB following error is seen:
FATAL: database "testdb" does not exist
DETAIL: The database subdirectory "base/xxxxx" is missing.
It seems this is know behavior, the code comment in dbcommands.d indicates that:
/*
* Force synchronous commit, thus minimizing the window between removal of
* the database files and commital of the transaction. If we crash before
* committing, we'll have a DB that's gone on disk but still there