Unit tests should be added for all publicly exposed APIs

[reazulhoque]

For all interfaces, dppl and dppl.ocldrv we should add unit tests to make sure the functions are behaving correctly.

[PokhodenkoSA]

I think we should use test coverage or do manual collecting of not tested APIs.

[diptorupd]

I am closing this issue as it is too broad and our test suites have improved significantly since the ticket was opened. We should raise tickets for specific functions based on coverage analysis.