Adding jest tests to nwb project

add-jest-to-nwb.sh

yarn add -D jest babel-jest babel-preset-es2015 babel-preset-react react-test-renderer
#Edit package.json adding the jest command : 
"scripts": {
  "build": "nwb build-react-component",
  "clean": "nwb clean-module && npm clean-demo",
  "start": "nwb serve-react-demo",
  "test": "nwb test",
  "test:coverage": "nwb test --coverage",
  "test:watch": "nwb test --server",
  "test:jest": "jest"
},

# For most setups this should be enough, for tweaking check below

# And add jest config ( OPTIONAL )
  "jest": {
    "scriptPreprocessor": "<rootDir>/node_modules/babel-jest",
    "testFileExtensions": [
      "js"
    ],
    "moduleFileExtensions": [
      "js",
      "json",
      "jsx"
    ]
  }