Add test utils

[apiv]

Adds test utils which stub out all entities-wrapped components.

This is easily implemented in either jest or karma+webpack.

The new export has functions:

• entities.mock(componentName: string, propsToProvide: {}) Whenever a component named componentName is encountered, it will be given the propsToProvide as props instead of wrapping with redux.
• entities.stub is entityStub from the frontend app.
• entities.reset resets the stubs.
• entities is the fake HOC

This allows you to write tests like this:

MyComponent.js

import entities from 'entities'

const MyComponent = () => /* ... */

export default entities({ bucketResource: { type: 'bucket' } })(MyComponent)

MyOtherComponent

import MyComponent from './MyComponent'

const MyOtherComponent = () => {
  return (
    <MyComponent />
  )
}

export default MyOtherComponent

MyOtherComponent.spec.js

import MyOtherComponent from './MyOtherComponent'
jest.mock('entities')
import entities from 'api-entities'

describe('MyOtherComponent', () => {
  beforeEach(() => {
    entities.reset()
    // give all instances of MyComponent these props:
    const props = {
      bucketResource: entities.stub({
        items: f.createList('Bucket', 4)
      })
    }
    entities.mock(MyComponent, props)
  })

  it('renders', () => {
    const component = mount(MyOtherComponent)
    // wooh! it renders without any redux errors! (because redux is never being used!)
    expect(component.find('MyComponent').props).toMatchObject(props)
  })
})

[apiv]

In webpack+karma, we would alias entities/components/Entities to entities/test-utils/mockEntities

[mjniday]

This looks good

[Brantron]

It looks good to me, I wonder if the test suite will be noticeably faster?

[apiv]

This should include docs on usage.

[codecov-io]

Codecov Report

Merging #9 into master will increase coverage by 0.42%.
The diff coverage is 90.32%.

@@            Coverage Diff             @@
##           master       #9      +/-   ##
==========================================
+ Coverage   83.03%   83.45%   +0.42%     
==========================================
  Files          17       18       +1     
  Lines         501      532      +31     
  Branches      150      167      +17     
==========================================
+ Hits          416      444      +28     
- Misses         71       73       +2     
- Partials       14       15       +1

Impacted Files	Coverage Δ
src/test-utils/mockEntities.js	90.32% <90.32%> (ø)

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