Function lookForOutput

npm_modules/cli/test/helpers/AsyncHelpers.ts:48–113

(
  { stdout = [], stderr = [], idleTimeoutMs }: { stdout?: (string | RegExp)[]; stderr?: (string | RegExp)[]; idleTimeoutMs?: number },
  subcommand: SubCommand,
)

 * Rejects if there are queries remaning after the
 */
export function lookForOutput(
  { stdout = [], stderr = [], idleTimeoutMs }: { stdout?: (string | RegExp)[]; stderr?: (string | RegExp)[]; idleTimeoutMs?: number },
  subcommand: SubCommand,
): Promise<true> {
  const [idleTimer, touch, complete] = timeoutOnIdle(idleTimeoutMs);

  const monitor = (requiredQueries: (string | RegExp)[]) => {
    let queries = requiredQueries.slice();
    let onDone: (value: true) => void, onError: (error: Error) => void;

    const promise = new Promise((resolve, reject) => {
      onDone = resolve;
      onError = reject;

      // If queries are empty to start with resolve immediately
      if (queries.length === 0) {
        resolve(true);
      }
    });

    const isDone = () => queries.length === 0;

    return {
      promise,
      isDone,
      onEachLine: onEachLine(line => {
        touch();
        queries = queries.filter((query): boolean => {
          if (typeof query === 'string') {
            return !line.toString().includes(query);
          }
          if (query instanceof RegExp) {
            return !query.test(line.toString('utf8'));
          }
          onError(new Error('invalid query'));
          return false;
        });

        if (isDone()) {
          onDone(true);
          return;
        }
      }),
    };
  };

  const stdoutMonitor = monitor(stdout);
  const stderrMonitor = monitor(stderr);

  subcommand.process.stdout.compose(stdoutMonitor.onEachLine).pipe(process.stdout);
  subcommand.process.stderr.compose(stderrMonitor.onEachLine).pipe(process.stderr);

  return Promise.race([
    idleTimer,
    subcommand
      .wait()
      .then((): true => {
        const allFound = [stderrMonitor, stderrMonitor].every(monitor => monitor.isDone());