title: classnames_1.default is not a function when testing with Jest
body: <p>I am facing issue with running test cases on <strong>Jest</strong> when classnames ( <a href="https://www.npmjs.com/package/classnames" rel="nofollow noreferrer">https://www.npmjs.com/package/classnames</a> ) library is being used :</p>
  
  <p>It throws error : <strong>classnames_1.default is not a function</strong></p>
  
  <p>It is working with webpack on website itself.. so i don't want to change import. </p>
  
  <p>I have an option to mock classnames for test to provide similar behaviour. Is there any other way to solve this issue ?</p>
  
  <p><strong>Has anyone faced this issue ?</strong></p>
  
  <p>Here is my jest configuration in package.json :</p>
  
  <p><code>"jest": {
      "globals": {
        "API_HOST": "",
        "DEV": false
      },
      "transform": {
        ".(ts|tsx)": "&lt;rootDir&gt;/node_modules/XXX-framework/jestTypeScriptPreProcessor.js"
      },
      "testRegex": "(/tests/.*|\.(test|spec))\.(js|jsx|ts|tsx)$",
      "transformIgnorePatterns": [],
      "moduleFileExtensions": [
        "ts",
        "tsx",
        "js",
        "json"
      ],
      "automock": false,
      "clearMocks": true,
      "resetMocks": true,
      "coverageThreshold": {
        "global": {
          "branches": 50,
          "functions": 50,
          "lines": 50,
          "statements": 50
        }
      },
      "modulePaths": [
        "&lt;rootDir&gt;/src",
        "&lt;rootDir&gt;/node_modules/XXX-framework/src"
      ],
      "unmockedModulePathPatterns": [
        "&lt;rootDir&gt;/node_modules/react/",
        "&lt;rootDir&gt;/node_modules/react-dom/",
        "&lt;rootDir&gt;/node_modules/react-addons-test-utils/",
        "&lt;rootDir&gt;/node_modules/enzyme/",
        "&lt;rootDir&gt;/node_modules/XXX-framework/"
      ]
    }</code></p>
  
  <p>Thanks</p>