@studyportals/cypress-slicer/plugin.js

Cypress plugin to slice the specPattern list of tests into subsets

const glob = require("glob");
const logger = require("./lib/logger")

/**
 * Selects only a subset of the files in the glob pattern.
 * @param {Cypress.ConfigOptions} config
 */
function cypressSlicerPlugin(config) {
  if (!config || !config.env) {
    return config;
  }

  if (!config.specPattern) {
    throw new Error(
      "Incompatible Cypress version detected; requires Cypress 10.0.0+"
    );
  }

  const { env } = config;

  const workers = Number(env.workers) || 1;
  const worker = Number(env.worker) || 1;

  if (worker >= 1 && worker <= workers) {
    if (workers > 1) {
      logger.log(`cypress-slicer: running worker ${worker} of ${workers}`);
    }
  } else {
    throw new Error(
      `cypress-slicer: invalid worker number ${worker} of ${workers}`
    );
  }

  const { specPattern, excludeSpecPattern } = config;

  const specFiles = [...specPattern].reduce((acc, pattern) => {
    const files = glob.sync(pattern, { ignore: excludeSpecPattern });
    return [...acc, ...files];
  }, []);

  const testCounter = specFiles.length;
  logger.log(`cypress-slicer: found a total of ${testCounter} spec files`);

  const chunks = (a, size) => {
    a = a.sort();
    return Array.from(new Array(Math.ceil(a.length / size)), (_, i) =>
      a.slice(i * size, i * size + size)
    );
  };

  let noTests = Math.ceil(testCounter / workers);

  const filteredSpecFiles = chunks(specFiles, noTests)[worker - 1];

  logger.log(`cypress-slicer: running ${filteredSpecFiles.length} spec files`);

  if (filteredSpecFiles.length) {
    config.specPattern = filteredSpecFiles;
  } else {
    throw new Error("cypress-slicer: Could not select any spec files");
  }

  return config;
}

module.exports = cypressSlicerPlugin;