under-the-hood of test runner: parsing builder.js

const builder = (yargs) => {
  // cli/run.js builder()
  return yargs
    .options({
      config: {
        config: true,
        description: "Path to config file",
      },
      reporter: {
        default: defaults.reporter,
        description: "Specify reporter to use",
        requiresArg: true,
      },
      ui: {
        default: defaults.ui,
        description: "Specify user interface",
        requiresArg: true,
      },
    })
    .check((argv) => {
      // lib/cli/run-helpers.js handleRequires
      // load --requires first, because it can impact "plugin" validation

      // lib/cli/run-helpers.js validatePlugin
      // validate `--reporter` and `--ui`.  Ensures there's only one, and asserts that it actually exists
      // Checks keys on Mocha.reporters + Mocha.interfaces

      return true;
    });
};
const handler = async function (argv) {
  const mocha = new Mocha(argv);

  try {
    // NEXT PHASE
    await runMocha(mocha, argv);
  } catch (err) {
    console.error("\n" + (err.stack || `Error: ${err.message || err}`));
    process.exit(1);
  }
};
const commands = {
  run: {
    command: ["$0 [spec..]", "inspect"],
    describe: "Run tests with Our-Mocha",
    builder,
    handler,
  },
};