Rails 5.1 webpacker config for react + jest + enzyme

.babelrc

{
  "presets": [
    [
      "env",
      {
        "modules": false,
        "targets": {
          "browsers": "> 1%",
          "uglify": true
        },
        "useBuiltIns": true
      }
    ],
    "react",
    "es2015"
  ],
  "plugins": [
    "syntax-dynamic-import",
    [
      "transform-class-properties",
      {
        "spec": true
      }
    ],
    "transform-object-rest-spread"
  ]
}

package.json

{
  "name": "jester",
  "private": true,
  "license": "UNLICENSED",
  "engines": {
    "node": "6.11.2"
  },
  "scripts": {
    "test": "jest"
  },
  "dependencies": {
    "autoprefixer": "^7.1.2",
    "babel-core": "^6.26.0",
    "babel-loader": "7.x",
    "babel-plugin-syntax-dynamic-import": "^6.18.0",
    "babel-plugin-transform-class-properties": "^6.24.1",
    "babel-plugin-transform-object-rest-spread": "^6.26.0",
    "babel-polyfill": "^6.26.0",
    "babel-preset-env": "^1.6.0",
    "babel-preset-es2015": "^6.24.1",
    "babel-preset-react": "^6.24.1",
    "classnames": "^2.2.5",
    "coffee-loader": "^0.7.3",
    "coffee-script": "^1.12.7",
    "compression-webpack-plugin": "^1.0.0",
    "core-js": "^2.5.0",
    "css-loader": "^0.28.4",
    "extract-text-webpack-plugin": "^3.0.0",
    "file-loader": "^0.11.2",
    "form-serialize": "^0.7.2",
    "gangway": "^2.2.0",
    "glob": "^7.1.2",
    "history": "^4.6.3",
    "immutable": "^3.8.1",
    "js-yaml": "^3.9.1",
    "microcosm": "^12.10.0",
    "node-sass": "^4.5.3",
    "path-complete-extname": "^0.1.0",
    "postcss-loader": "^2.0.6",
    "postcss-smart-import": "^0.7.5",
    "precss": "^2.0.0",
    "promise": "^8.0.1",
    "prop-types": "^15.5.10",
    "rails-erb-loader": "^5.1.0",
    "react": "^15.6.1",
    "react-autocomplete": "^1.7.1",
    "react-dom": "^15.6.1",
    "react-guard": "^0.5.0",
    "react-immutable-proptypes": "^2.1.0",
    "react-modal": "^2.2.4",
    "react-router": "^4.1.2",
    "react-router-dom": "^4.1.2",
    "react-switch-button": "^2.2.2",
    "resolve-url-loader": "^2.1.0",
    "sass-loader": "^6.0.6",
    "style-loader": "^0.18.2",
    "superagent": "^3.5.2",
    "titlecase": "^1.1.2",
    "webpack": "^3.5.5",
    "webpack-manifest-plugin": "^1.3.1",
    "webpack-merge": "^4.1.0"
  },
  "devDependencies": {
    "babel-jest": "^20.0.3",
    "enzyme": "^2.9.1",
    "jest": "^20.0.4",
    "jest-css-modules": "^1.1.0",
    "react-test-renderer": "^15.6.1",
    "webpack-dev-server": "^2.7.1"
  },
  "jest": {
    "roots": [
      "app/javascript/__tests__/"
    ],
    "moduleDirectories": [
      "node_modules",
      "app/javascript",
      "app/javascript/__tests__"
    ],
    "moduleNameMapper": {
       "\\.(s?css)$": "<rootDir>/node_modules/jest-css-modules"
     }
  }
}