Testing Actions

State Change
Testing for a state change is easy, and you can just run your action like a function.
1
import { effects } from 'ferp';
2
​
3
const IncrementCounter = state => [
4
  { ...state, counter: state.counter + 1 },
5
  effects.none(),
6
];
7
​
8
describe('IncremenetCounter', () => {
9
  it('increments the counter state variable', () => {
10
    const initialState = { counter: 0 };
11
    
12
    const [state, _effect] = IncrementCounter(initialState);
13
    
14
    expect(state).toDeepEqual({
15
      counter: 1,
16
    });
17
  });
18
});
Copied!
Testing action builders is very similar, too:
1
import { effects } from 'ferp';
2
​
3
const IncrementCounterByN = n => state => [
4
  { ...state, counter: state.counter + n },
5
  effects.none(),
6
];
7
​
8
describe('IncremenetCounterByN', () => {
9
  it('increments the counter state variable using the provided value', () => {
10
    const initialState = { counter: 0 };
11
    
12
    const [state, _effect] = IncrementCounterByN(999)(initialState);
13
    
14
    expect(state).toDeepEqual({
15
      counter: 999,
16
    });
17
  });
18
});
Copied!
Result of Side-Effects
Testing that the correct side effects can be a little more tricky. The problem is that effects touch the outside world that is not controlled by Ferp. Running these end-to-end just like the effect testing is likely your best bet.
actions.spec.js
actions.js
todoFx.js
1
import * as sinon from 'sinon';
2
import { app } from 'ferp';
3
​
4
import * as actions from './actions.js';
5
​
6
describe('RequestTodo', () => {
7
  it('does not modify the state', () => {
8
    const initialState = { todos: [], externals: { fetch: window.fetch } };
9
    
10
    const [state] = actions.RequestTodo(1)(initialState);
11
    
12
    expect(state).toBe(initialState);
13
  });
14
  
15
  it('successfully fetches a todo', (done) => {
16
    const expectedTodo = { id: 1, text: 'foo', completed: false };
17
    const fakeFetch = sinon.fake((arg) => {
18
      return {
19
        json: Promise.resolve(expectedTodo)
20
      };
21
    });
22
    const initialState = { todos: [], externals: { fetch: fakeFetch } };
23
    
24
    const expectedTodosInOrder = [
25
      [], // init
26
      [], // request
27
      [expectedTodo], // on success
28
    ];
29
    
30
    app({
31
      init: actions.RequestTodo(expectedTodo.id)(initialState),
32
      observe: ([state, effect]) => {
33
        expect(state.todos)
34
          .toDeepEqual(expectedTodosInOrder.unshift());
35
          
36
        if (expectedTodosInOrder.length === 0) {
37
          done();
38
        }
39
      },
40
    });
41
  });
42
});
Copied!
1
import { effects } from 'ferp';
2
import * as todoFx from './todoFx.js';
3
​
4
export const AddTodo = (todo) => (state) => [
5
  { ...state, todos: state.todos.concat(todo) },
6
  effects.none(),
7
];
8
​
9
export const RequestTodo = (todoId) => (state) => [
10
  state,
11
  todoApi.getTodo(state.external.fetch, todoId, AddTodo),
12
];
Copied!
1
import { effects } from 'ferp';
2
​
3
export const getTodo = (fetchFn, id, onSuccess, onFailure) => effects.defer(
4
  fetchFn(`https://jsonplaceholder.typicode.com/todos/${id}`)
5
    .then(response => response.json())
6
    .then(data => effects.act(onSuccess(data)))
7
    .catch((err) => (
8
      onFailure
9
        ? effects.act(onFailure(err))
10
        : effects.none()
11
    ))
12
);
Copied!
Yes, that test code looks clunky, so why not make a helper to make things a little easier?
support/endToEndTest.js
1
import { app } from 'ferp';
2
​
3
export const endToEndTest = (init, assertions, done) => app({
4
  init,
5
  observe: (...args) => {
6
    const assertion = assertions.unshift();
7
    assertion(...args);
8
    if (assertions.length === 0) {
9
      done();
10
    }
11
  },
12
});
Copied!
Which would result in:
actions.spec.js
1
import { endToEndTest } from './support/endToEndTest.js';
2
​
3
// ...
4
​
5
  it('successfully fetches a todo', (done) => {
6
    const expectedTodo = { id: 1, text: 'foo', completed: false };
7
    const fakeFetch = sinon.fake((arg) => {
8
      return {
9
        json: Promise.resolve(expectedTodo)
10
      };
11
    });
12
    const initialState = { todos: [], externals: { fetch: fakeFetch } };
13
    
14
    endToEndTest(
15
      actions.RequestTodo(expectedTodo.id)(initialState),
16
      [
17
        ([state]) => expect(state.todos).toDeepEqual([]), // init
18
        ([state]) => expect(state.todos).toDeepEqual([]), // request
19
        ([state]) => expect(state.todos).toDeepEqual([expectedTodo]), // on success
20
      ],
21
      done
22
    );
23
  });
Copied!
There may be other forms of helpers that can make the end-to-end portions of your tests to be more readable and manageable.

Understanding Actions in Ferp - Previous

Writing Your Own Actions

Next - Understanding Subscriptions in Ferp

What is a Ferp Subscription?

Last modified 8mo ago

Copy link

Contents

State Change

Result of Side-Effects