Testing a HTTP Error Handler Utility Hook

Testing (Series)
Understanding Unit Test From The Best Book On The Topic
Testing Ag-Grid React’s Custom Cell Renderer Component
Testing ErrorFallback Component
Testing useDebouncedValue Hook
Testing a HTTP Client Adaptor Hook useClient
Testing a HTTP Error Handler Utility Hook
Testing a Generic Fetch Item List hook with Mock Service
Introducing @mockapi/msw, mock an API server for your entities without writing any code with Mock Service Worker
Testing a Generic Save Item Hook with MSW and @mockapi/msw
Testing a Text Field component integrating Mui’s Text Field with React Hook Form

Subject Under Test

A utility hook provides an HTTP error handler that sends errors to a message context. A message snack bar component would show errors in toasters for end users.

Behaviours

1. it takes an optional message to be prepended to error messages returned from the server
2. it takes an optional translator for localisation
3. it clears the JWT token if the server returns 401 Unauthorised Error
4. it sends an error alerting the user to log in to an account with the required permissions if the server returns 403 Unauthorised Error
5. it sends extract error messages from response.data when applicable
6. it sends “Server connection failed” if no response is received
7. if the above fails, it logs out error as-is in the console

Code

Notes

1. TestComponent shows a way the error handler hook could be used. It is a component designed to facilitate the tests.
2. setup function mocks axios and renders the above component inside a MessageProvider which is not mocked.
3. userEvent is used to trigger the HTTP call, which was mocked to reject with an error object. It has to be wrapped inside an act block as it updates the states in the message context.
4. findBy queries from @testing-library is async by design, and we do not have to do anything extra in the tests to wait for async operations.
5. in the last test, I use `waitFor` from `@testing-library` as there is nothing be found by `findBy`. Note: do not forget to `await` for `waitFor` as I did.

Originally published at https://dev.to on January 11, 2022.