Improve test cases - Migrate to unit test cases

[DevAhamed]

At the time of v1.2.6 release, the combined test coverage stands at 55%. These include some false positive test cases as well. Since we have android unit test which needs emulator to boot up, our CI build times are high and fail most of the times. So its time to improve the test cases for the library.

• Convert all test cases into jUnit tests
• Remove the false positive test cases
• Increase the coverage at least to 80%

[DevAhamed]

Progress update

Android instrumentation test cases are removed from the library. But still we are able improve the coverage from 55% to 74% (at the time v2.0.0-alpha01).

All test cases are written from scratch again. Most of the false positives are removed. I am still working on improving the quality of test cases.