Mastering React Test-Driven Development

Handling the redo action

Redo is very similar to undo, just reversed. In our production code, however, we'll need to add a switch statement:

1. First, add a new definition for the UNDO action, in the top-level describe block:

describe('withUndoRedo', () => {  const undoAction = { type: 'UNDO' };  const redoAction = { type: 'REDO' };  ...});

2. Underneath the undo describe block, add the following redo describe block with the first test. Be careful with the setup for the spy; the call is mockReturnValueOnce here, not mockReturnValue. The test needs to ensure it takes its value from the stored redo state:

describe('redo', () => {  let newState;  beforeEach(() => {    decoratedReducerSpy.mockReturnValueOnce(future); newState = reducer(present, innerAction); ...