user service tests

[Devesh21700Kumar]

Add interfaces and unit tests for the user services

npm run test success result

• My code follows the code style of this project.
• I have updated the documentation accordingly.
• All new and existing tests passed.
• My changes generate no new warnings
• The title of my pull request is a short description of the requested changes.

reference from https://github.com/jmcdo29/testing-nestjs/blob/master/apps/mongo-sample/src/cat/cat.service.spec.ts

[Devesh21700Kumar]

@Abhishek-kumar09 the user service tests with its interfaces and the basis setup for future tests