# Testing

The main parts we want to unit test in Vuex are mutations and actions.

### Testing Mutations

Mutations are very straightforward to test, because they are just functions that completely rely on their arguments. One trick is that if you are using ES2015 modules and put your mutations inside your `store.js` file, in addition to the default export, you can also export the mutations as a named export:

``` js
const state = { ... }

// export mutations as a named export
export const mutations = { ... }

export default new Vuex.Store({
  state,
  mutations
})
```

Example testing a mutation using Mocha + Chai (you can use any framework/assertion libraries you like):

``` js
// mutations.js
export const INCREMENT = state => state.count++
```

``` js
// mutations.spec.js
import { expect } from 'chai'
import { mutations } from './store'

// destructure assign mutations
const { INCREMENT } = mutations

describe('mutations', () => {
  it('INCREMENT', () => {
    // mock state
    const state = { count: 0 }
    // apply mutation
    INCREMENT(state)
    // assert result
    expect(state.count).to.equal(1)
  })
})
```

### Testing Actions

Actions can be a bit more tricky because they may call out to external APIs. When testing actions, we usually need to do some level of mocking - for example, we can abstract the API calls into a service and mock that service inside our tests. In order to easily mock dependencies, we can use Webpack and [inject-loader](https://github.com/plasticine/inject-loader) to bundle our test files.

Example testing an async action:

``` js
// actions.js
import shop from '../api/shop'

export const getAllProducts = ({ dispatch }) => {
  dispatch('REQUEST_PRODUCTS')
  shop.getProducts(products => {
    dispatch('RECEIVE_PRODUCTS', products)
  })
}
```

``` js
// actions.spec.js

// use require syntax for inline loaders.
// with inject-loader, this returns a module factory
// that allows us to inject mocked dependencies.
import { expect } from 'chai'
const actionsInjector = require('inject!./actions')

// create the module with our mocks
const actions = actionsInjector({
  '../api/shop': {
    getProducts (cb) {
      setTimeout(() => {
        cb([ /* mocked response */ ])
      }, 100)
    }
  }
})

// helper for testing action with expected mutations
const testAction = (action, args, state, expectedMutations, done) => {
  let count = 0
  // mock dispatch
  const dispatch = (name, ...payload) => {
    const mutation = expectedMutations[count]
    expect(mutation.name).to.equal(name)
    if (payload) {
      expect(mutation.payload).to.deep.equal(payload)
    }
    count++
    if (count >= expectedMutations.length) {
      done()
    }
  }
  // call the action with mocked store and arguments
  action({dispatch, state}, ...args)

  // check if no mutations should have been dispatched
  if (expectedMutations.length === 0) {
    expect(count).to.equal(0)
    done()
  }
}

describe('actions', () => {
  it('getAllProducts', done => {
    testAction(actions.getAllProducts, [], {}, [
      { name: 'REQUEST_PRODUCTS' },
      { name: 'RECEIVE_PRODUCTS', payload: [ /* mocked response */ ] }
    ], done)
  })
})
```

### Running Tests

If your mutations and actions are written properly, the tests should have no direct dependency on Browser APIs after proper mocking. Thus you can simply bundle the tests with Webpack and run it directly in Node. Alternatively, you can use `mocha-loader` or Karma + `karma-webpack` to run the tests in real browsers.

#### Running in Node

Create the following webpack config:

``` js
module.exports = {
  entry: './test.js',
  output: {
    path: __dirname,
    filename: 'test-bundle.js'
  },
  module: {
    loaders: [
      {
        test: /\.js$/,
        loader: 'babel',
        exclude: /node_modules/
      }
    ]
  },
  babel: {
    presets: ['es2015']
  }
}
```

Then:

``` bash
webpack
mocha test-bundle.js
```

#### Running in Browser

1. Install `mocha-loader`
2. Change the `entry` from the Webpack config above to `'mocha!babel!./test.js'`.
3. Start `webpack-dev-server` using the config
4. Go to `localhost:8080/webpack-dev-server/test-bundle`.

#### Running in Browser with Karma + karma-webpack

Consult the setup in [vue-loader documentation](http://vuejs.github.io/vue-loader/workflow/testing.html).
