Generate batched tests for karma-webpack

build-tests.js

const path = require('path');
const Promise = require('bluebird');
const readdir = Promise.promisify(require('fs').readdir);
const stat = Promise.promisify(require('fs').stat);
const writeFile = Promise.promisify(require('fs').writeFile);
const recurse = Promise.promisify(require('recursive-readdir'));

const backSlashRegex = /\\{1,2}/g;

// A list of files that should always be included in the test files
// these will be included before the tests so you can register setup and
// teardown functions
const includes = [
  '../setup.js',
];

function getPath(relative) {
  return path.resolve(__dirname, relative);
}

function getRelativeFilePath(dir, file) {
  if (file.startsWith('.')) {
    return file;
  }

  // replace backslash with forward slash when using windows systems
  return `./${path.relative(dir, file).replace(backSlashRegex, '/')}`;
}

function getRequires(dir, paths) {
  // Generate a list of require calls
  return paths.map(item => `require('${getRelativeFilePath(dir, item)}');`)
  .join(' ');
}

function writeTestFile(relativeDir, files) {
  const dir = getPath(relativeDir);
  // The name of the file to generate, this is passed to karma
  // This should also be added to .gitignore
  const writeFilePath = path.join(dir, 'generated_test.js');

  // group the tests in a mocha describe
  const content =
  `/* eslint-disable */
    describe('${relativeDir}', function tests() {
      ${getRequires(dir, includes)}
      ${getRequires(dir, files)}
    });
    /* eslint-enable */`;

  console.log(`Writing test file - ${writeFilePath}`);

  return writeFile(writeFilePath, content);
}

function build() {
  // Read the test directory and find all child directories
  return readdir(__dirname)
  .filter(item => {
    // Skip any directories that don't contain test files
    // this could be done with a glob or regex for more complex setups
    if (item === 'helpers') {
      return false;
    }

    // Check if the path is a directory
    return stat(getPath(item))
    .then(file => file.isDirectory());
  })
  .then(items => {
    // Build up a map of promises for lists of javascript files
    // Whatever pattern test files take in the system could be used here
    const dirs = {};
    items.forEach(item => {
      dirs[item] = recurse(getPath(item), ['!*.js']);
    });

    // resolve the file path lists
    return Promise.props(dirs);
  })
  .then(dirs => {
    // Asynchronously write the test files
    // This could also be done using map with concurrency to increase speed
    const keys = Object.keys(dirs);
    return Promise.each(keys, item => writeTestFile(item, dirs[item]));
  });
}

module.exports = build().tap(files => console.log(`${files.length} test files created`));

package.json

{
  "dependencies": {
    "bluebird": "3.5.0",
  },
  "devDependencies": {
    "recursive-readdir": "2.2.1",
  },
  "scripts": {
    "build": "node ./test/build-tests.js",
    "test": "npm run build && karma start"
  }
}