reduceActions

Testing helper. Calculates the state after dispatching an sequence of actions to a specific reducer, starting from the initial state.

// JavaScript
function reduceActions(reducer, ...actions)
// TypeScript
function reduceActions<S, A extends Action, AS extends A[]>(
reducer: Reducer<S, A>,
...actions: AS
): S

Details

reduceActions calls reducer with each of the passed actions - as if these had been dispatched in the specified order - and returns the resulting state. For the first reducer call, the reducer's initial state (as determined by getInitialState) is used; each following call receives the state returned by the previous one.

If called without any actions, reduceActions simply returns the reducer's initial state - that is, reduceActions(reducer) is equivalent to getInitialState(reducer).

This helper is meant for use in reducer tests.

Examples

Basic usage:

import { reduceActions } from 'redux-preboiled'
const reducer = (state = 0, action) => {
switch (action.type) {
case 'increment':
return state + 1
case 'multiply':
return state * action.payload
default:
return state
}
}
reduceActions(reducer, { type: 'increment' })
// => 1
reduceActions(
reducer,
{ type: 'increment' },
{ type: 'increment' },
{ type: 'multiply', payload: 2 }
)
// => 4
reduceActions(reducer)
// => 0

Usage in a Jest test:

import { reduceActions } from 'redux-preboiled'
import counterReducer, {
increment,
multiply
} from './counter.redux'
test('increment', () => {
const state = reduceActions(counterReducer, increment())
expect(state).toEqual(1)
})
test('increment and multiply', () => {
const state = reduceActions(
counterReducer,
increment(),
increment(),
multiply(4)
)
expect(state).toEqual(8)
})

See Also