Improve Testing

[ayushr2]

Currently, the tests do not test the following:

• The DB contents after jobs have been scheduled/executed or after courses are uploaded.
• Worker node failure. We will have to mock the variable which decided how often the heartbeat validator runs and we can make the testing thread to sleep (after polling a job) and then check DB contents to assert that the job is marked as failed.
• Worker node state (alive/dead)