title: Jest Test Babel Error: Plugin/Preset files are not allowed to export objects
body: <p>I'm using a very up-to-date <em>(December 2017)</em> stack of dependencies. As I try-out isomorphic react tests with Jest, the test suit keeps failing with the following error:</p>
  
  <pre><code>* Test suite failed to run
  [BABEL] /__tests__/router.test.js: Plugin/Preset files are not allowed to
  export objects, only functions.
  </code></pre>
  
  <p>Here are my dependencies:</p>
  
  <pre><code>"dependencies": {
      "axios": "^0.17.1",
      "babel-polyfill": "^6.26.0",
      "cors": "^2.8.4",
      "express": "^4.16.2",
      "react": "^16.1.1",
      "react-dom": "^16.1.1",
      "react-router-dom": "^4.2.2"
    },
    "devDependencies": {
      "@babel/core": "^7.0.0-beta.35",
      "babel-cli": "^6.26.0",
      "babel-core": "^7.0.0-bridge.0",
      "babel-eslint": "^8.0.2",
      "babel-jest": "^22.0.1",
      "babel-loader": "^7.1.2",
      "babel-preset-env": "^1.6.1",
      "babel-preset-react": "^6.24.1",
      "enzyme": "^3.2.0",
      "enzyme-adapter-react-16": "^1.1.0",
      "enzyme-to-json": "^3.2.2",
      "eslint": "^4.11.0",
      "eslint-plugin-react": "^7.5.1",
      "html-webpack-plugin": "^2.30.1",
      "jest": "^21.2.1",
      "nodemon": "^1.11.0",
      "parallelshell": "^3.0.2",
      "react-test-renderer": "^16.2.0",
      "regenerator-runtime": "^0.11.1",
      "supertest": "^3.0.0",
      "webpack": "^3.8.1",
      "webpack-dev-server": "^2.9.4"
    },
    "peerDependencies": {
      "babel-core": "^7.0.0-0"
    }
  </code></pre>
  
  <p>.babelrc :</p>
  
  <pre><code>{
    "presets": [
      "env",
      "react",
    ]
  }
  </code></pre>
  
  <p>Does anyone have any insights as to why Jest won't run? </p>