add coverage to the test

[piyusql]

Is your feature request related to a problem? Please describe.

currently we do unit tests for each module, we should add coverage such that we will be knowing that how much code has been covered by the test cases.
it will eventually improve our code quality and eventually it will avoid any regressions in long run.

Describe the solution you'd like

coverage is a good library to be used

Describe alternatives you've considered

No response

Additional context

No response