Testem receiving imports compiled to `require` when using ES2015/React presets to Babel

I have a project which is set up so that it builds with reactand jsx. It works fine to build it using node_modules/webpack/bin/webpack.js --config webpack.config.js and I can run the result in the browser with no problems. However, when I run npm test and view the test runner in the browser, I get the error: "Uncaught ReferenceError: require is not defined at dashboard-tests.js:3". It seems that webpack is compiling my tests (but not my normal code) into a version of javascriptthat can't be run in browsers.

Here are the relevant files:

.babelrc:

{
   "presets": ["es2015", "react"]
}

testem.json:

{
  "framework": [
    "jasmine"
  ],
  "launch_in_dev": [
    "PhantomJS"
  ],
  "launch_in_ci": [
    "PhantomJS"
  ],
  "serve_files": [
    "tmp/**/*-test{,s}.js"
  ],
  "on_start": "babel static_source --out-dir tmp",
  "on_exit": "yes | rm -r tmp"
}

package.json:

{
  "main": "index.js",
  "scripts": {
    "test": "testem"
  },
  "dependencies": {
    "jquery": "^3.2.1",
    "prop-types": "^15.6.0",
    "react": "^16.0.0",
    "react-dom": "^16.0.0",
    "react-feather": "^1.0.7"
  },
  "devDependencies": {
    "babel-cli": "^6.26.0",
    "babel-core": "^6.26.0",
    "babel-loader": "^7.1.2",
    "babel-preset-env": "^1.6.1",
    "babel-preset-react": "^6.24.1",
    "jasmine-es6": "^0.4.3",
    "testem": "^1.18.4",
    "webpack": "^3.6.0"
  }
}

webpack.config.js:

var path = require("path");
var webpack = require('webpack');

module.exports = {
  context: __dirname,
  entry: './static_source/js/index.js', 
  output: {
    path: path.resolve('./app/static/js/'),
    filename: "compiled.js"
  },
  plugins: [],
  module: {
    loaders: [
      { test: /\.js$/, loader: 'babel-loader', exclude: /node_modules/ },
      { test: /\.jsx$/, loader: 'babel-loader', exclude: /node_modules/ }
    ],
  }
}

dashboard-tests:

import React from 'react';
import ReactDOM from "react-dom";
import TestUtils from "react-dom/test-utils";

import Dashboard from './dashboard';

describe('Dashboard', function() {
  it('exists', function() {
    expect(Dashboard).not.toBe(undefined);
  });

  it('renders arrows', function() {
    var dashboard = <Dashboard />;
    var renderedDashboard = TestUtils.renderIntoDocument(dashboard);

    var arrowsDiv = TestUtils.findRenderedComponentWithClass('arrows');

    expect(arrowsDiv).not.toBe(undefined);
  });
});

Solution

You are using Babel to compile your test source files. Babel is just a transpiler, it takes ES+ files and translates them to ES5 files. Because import does not exist in ES5 Babel replaces them with require().

To fix the problem you need to bundle your source file into one, using Webpack.

You will need a separate Webpack configuration file, let's call it webpack.config.test.js. In this file we need to instruct Webpack to fetch all your static_source/**/*-test{,s}.js files as entry-points. You will need the glob module : npm install glob --save-dev. Then add the webpack.config.test.js file with this content :

var path = require("path");
var glob = require('glob');
var webpack = require('webpack');

module.exports = {
  context: __dirname,
  // we look for all file ending with -test(s?).js and return the absolute path
  entry: glob
      .sync('./static_source/js/**/*-test{,s}.js')
      .map(function(file) { return path.resolve(__dirname, file) }),
  output: {
    // save the resulting bundle in the ./tmp/ directory
    path: path.resolve('./tmp/'),
    filename: "compiled.js"
  },
  plugins: [],
  module: {
    loaders: [
      { test: /\.js$/, loader: 'babel-loader', exclude: /node_modules/ },
      { test: /\.jsx$/, loader: 'babel-loader', exclude: /node_modules/ }
    ],
  }
}

On the testem.json file replace the on_start with a before_test to Webpack, and the serve_files to map to the bundled file.

"before_tests": "webpack --config webpack.config.test.js ",
"serve_files": [
    "tmp/compiled.js"
],

When testem will be launched it will trigger the Webpack test compilation. Now you should have a tmp/compiled.js file with all your test files bundled. You may need to do some tweaking but it should basically works.