Testing

Because your domain is described a series of pure functions, testing becomes ultra-simple: given some input, expect a certain output. No mocking calls to external services or a database. 
Actions
Let's look at the basic example from the Domain page:
actions.js
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const actions = {
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  addTodo: (state, payload) => {
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    if (!payload.title) throw new Error('titleMissing')
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    return [{
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      type: 'TodoAdded',
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      title: payload.title,
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      at: Date.now(),
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    }]
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  }
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}
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​
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module.exports = actions
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Now let's write a test for this.
__test__/actions.js
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// stub Date.now
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Date.now = () => 123
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​
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const test = require('tape')
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const actions = require('../actions')
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​
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test('addTodo', assert => {
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  assert.deepEquals(
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    actions.addTodo({}, { title: 'foobar' }),
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    [{
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      type: 'TodoAdded',
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      title: 'foobar',
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      at: 123
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    }],
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    'generates a TodoAdded event'
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  )
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  assert.throws(
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    () => actions.addTodo({}, { foo: 'bar' }),
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    /titleMissing/,
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    'throws if title is missing'
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  )
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})
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And we can even execute it:
​
Reducer
reducer.js
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const initialState = {
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  todos: []
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}
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​
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const reducer = (state, event) => {
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  switch (event.type) {
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    case 'TodoAdded':
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      return {
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        todos: [
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          ...state.todos,
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          { title: event.title },
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        ]
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      }
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    default:
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      return state
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  }
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}
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​
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module.exports = (events, state=initialState) => events.reduce(reducer, state)
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​
__test__/reducer.js
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const test = require('tape')
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const reducer = require('../reducer')
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​
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test('todoReducer', assert => {
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  const events = [
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    { type: 'TodoAdded', title: 'get milk' },
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    { type: 'TodoAdded', title: 'borrow sugar' },
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    { type: 'Invalid', title: 'ignore this' },
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  ]
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  const expected = {
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    todos: [
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      { title: 'get milk' },
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      { title: 'borrow sugar' },
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    ]
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  }    
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  const result = reducer(events)
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  assert.deepEquals(result, expected, 'reduces events')
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  assert.end()
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})
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Domain

Examples

Last modified 2yr ago

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Actions

Reducer

Actions

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Reducer