async function compareReporters(reporter) {
  const [actual, expected] = await Promise.all([
    runMochaAsync(REPORTER_FIXTURE_PATH, [
      '--reporter',
      reporter,
      '--no-parallel'
    ]),
    runMochaAsync(REPORTER_FIXTURE_PATH, ['--reporter', reporter, '--parallel'])
  ]);

  // the test duration is non-deterministic, so we just fudge it
  actual.output = expected.output = expected.output.replace(/\d+m?s/g, '100ms');

  return {actual, expected};
}
Run a test fixture with the same reporter in both parallel and serial modes,
returning both outputs for comparison
@param {string} reporter - Reporter name
@returns {{actual: import('../helpers').Summary, expected: import('../helpers').Summary}}