Testing a HTTP Error Handler Utility Hook

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.

Comments

[Jayesh Choudhary]

Thanks ... testing is often neglected and its hard to find good reading material on it .. appreciated :)

[Rex]

You are welcome. I am glad you liked it. There are a lot of misconceptions out there for testing, but also loads of good ones. Just that if one doesn’t have a good understanding of the principles of testing, it is not easy to recognise one.

If you look for a good testing book to read, read this one: manning.com/books/unit-testing. I think principles are at the core of effective testing.

I know testing is important but have been putting it off for so long, because I didn’t have a concrete understanding of what’s the correct way and to be frank I was confused. The book helped me tremendously.