Write automated test

[sanjeevyadavIT]

Is your feature request related to a problem? Please describe.
App doesn't contain test case as a result, new changes can break previous functionality. Unit, Integration and end-to-end test cases are required to make app robust and less error prone.

Describe the solution you'd like

1. Write simple unit test case
2. Write integration test
3. Write end-to-end test

Additional context
Use jest.js for unit & integration test
Use detox.js for end-to-end test