Testing Reducers Created with createSlice in Redux Toolkit
Reducers created with createSlice() can be easily tested by calling them directly with an initial state and an action. Since reducers are pure functions, you can verify that they produce the expected next state for a given input without needing to mock a Redux store.
Import the reducer and its action creators from the slice file.
Provide an initial state and simulate actions by dispatching them manually.
Assert that the returned state matches the expected output.
Ensure that reducers do not mutate the original state (immutability test).
By testing reducers in isolation, you ensure the logic for state transitions works correctly, making your Redux application more predictable and maintainable.