Theme switch doesn't work and test's fail

[ibayer]

Thanks for the example! Will trying it out (npm -version 6.4.1)

git clone https://github.com/react-theming/create-material-ui-app.git
cd create-material-ui-app
npm install
npm run storybook

I ran into two issues:

1. The rendered component don't change if I switch between light and dark theme.

2. The test fails

 FAIL  src/Storyshots.test.js
  ● Test suite failed to run

    Cannot find module '@storybook/addon-storyshots' from 'Storyshots.test.js'

    > 1 | const initStoryshots = require('@storybook/addon-storyshots').default
        |                        ^
      2 | initStoryshots()
      3 | 

      at Resolver.resolveModule (node_modules/jest-runtime/node_modules/jest-resolve/build/index.js:230:17)
      at Object.require (src/Storyshots.test.js:1:24)

 PASS  src/App.test.js

Test Suites: 1 failed, 1 passed, 2 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        1.167s
Ran all test suites.

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