Add tests

Is your feature request related to a problem? Please describe. As more and more functionalities are implemented in the project, we need to implement tests to assure the application is working as expected.

Describe the solution you'd like Following the project architecture, we want to test the following parts (and sub-parts) of our application

• Client
  • Shared components: Snapshots & unit tests
  • Helpers: Unit tests
  • Scenes: End to end tests
  • Services: Mocking + unit tests ?
• Server
  • Resolvers: Mocking + unit tests ?
  • Helpers: Unit tests
  • Integrations: Mocking + unit tests ?

Some useful links: https://github.com/APIs-guru/graphql-faker

Additional context As writing tests are often considered (wrongly) as a misuse of a developer's time, we need to favor the DX (developer experience): Writing a new test should be as simple as possible.