Learning Redux

Reducers

Just like synchronous action creators, reducers are pure functions. They accept the current state and an action object as arguments and return a new state. As a result, they are very easy to test—we simply compare the expected state after an action with the actual result of the reducer.

For simplicity, we are going to start with the filterReducer:

1. Create a new directory, which will contain all reducer-related tests: __tests__/reducers/.
2. Create a new file: __tests__/reducers/filter.test.js.
3. Import the filter-related action creators and the reducer:

import { setFilter, clearFilter } from '../../src/actions'import filterReducer from '../../src/reducers/filter'

Note that we cannot import the filterReducer directly from the reducers ...