1  import util from './reducer'
 2  
 3  describe('reducer utility', () => {
 4    const reducers = {
 5      TEST_ACTION: (state, payload) => ({
 6        ...state,
 7        ...payload,
 8      }),
 9    }
10  
11    const state = { foo: 'bar' }
12    const action = { type: 'TEST_ACTION', payload: { baz: true } }
13    const missingAction = { type: 'MISSING_ACTION' }
14    const reducer = util(reducers, state)
15  
16    test("it should return the existing state when the action doesn't exist", () => {
17      // Given an existing state
18      // And an action we can't reduce
19  
20      // We should expect the function to pass through the existing state
21      expect(reducer(state, missingAction)).toEqual({ foo: 'bar' })
22    })
23  
24    test('it should call the correct reducer when the action exists', () => {
25      // Given an existing state
26      // And an action we can reduce
27  
28      // We expect the function to return the correctly reduced new state
29      expect(reducer(state, action)).toEqual({
30        foo: 'bar',
31        baz: true,
32      })
33    })
34  
35    test('it should return the default state if the existing state is null', () => {
36      // Given a null state
37      // And an action we can't reduce
38  
39      // We expect the default state
40      expect(reducer(null, missingAction)).toEqual({ foo: 'bar' })
41    })
42  
43    test('it should return the existing state if the action is null', () => {
44      // Given a null state
45      // And an action that is undefined
46  
47      // We expect the default state
48      expect(reducer(state, undefined)).toEqual({ foo: 'bar' })
49    })
50  })