Mastering React Test-Driven Development

Completing the reducer

The Git tag for this section is customer-reducer.

We've completed our saga; now let's complete the reducer. It already partially handles the ADD_CUSTOMER_SUBMITTING action, but not quite. We'll start there and then move on to handling ADD_CUSTOMER_FAILED, ADD_CUSTOMER_VALIDATION_FAILED, and ADD_CUSTOMER_SUCCESSFUL:

1. Add this test to the ADD_CUSTOMER_SUBMITTING actions describe block. This test specifies typically expected behavior for reducer actions: any existing state should always be maintained:

it('maintains existing state', () => {  expect(reducer({ a: 123 }, action)).toMatchObject({    a: 123  });});

2. Make that pass by modifying the reducers as follows:

export const reducer = (state = defaultState, action) => {