Some ways to test a service that relies on a file watcher service and service bus. Service bus is merely a message delivery mechanism that guarantees messages will not be dropped and the sender and receiver (typically the client and the server) process these messages asynchronously.
1) Start copying a large file into the watched folder that takes a considerable time to copy.
2) Remove 'Everyone' or public access from the security settings of the watched folder.
3) Copy a file with extensions inclusive of the pattern being watched
4) Copy a file that triggers an exception in the servie such as a file with junk contents different from what is being expected
5) Send a message that causes an exception in the serve. If the server is expecting the path to a newly added file, send a path which denies access
6) Check the number of retries for the message in step 5)
7) For messages that repeatedly fail, check that the message made it to the poison queue.
8) Turn off the server that the messages are being received by and check the expiration of the messages and their move to dead letter queue.
9) Check the database for duplicate entries with same file name as the one in the watched folder
10) Check that the database entry for the same file input is refreshed on each attempt.
11) Check if this happens in a transaction where all the steps from moving a file, to clearing the message queue, to purging the database entry all occur in a rollback.
12) Check that the server processing the messages does not hang if the input doesn't contain what the server is looking for.
13) Check that the security settings on the file, folder, queue access, database and other dependencies are changed and don't cause service failures.
14) Check that queue cannot be flooded with unprocessed messages or denial of service attacks.
15) Check that watched folder does not have a backlog of files.