code: func assertNotExists(p string) []error {
  	var errs []error
  	e, err := fileExists(p)
  	if err != nil {
  		errs = append(errs, fmt.Errorf("error checking %q exists: %v", p, err))
  	}
  	if e {
  		errs = append(errs, fmt.Errorf("file %q exists unexpectedly", p))
  	}
  	return errs
  }
docs: // assertNotExists asserts that a file at the given path does not exist. A
  // non-empty list of errors is returned if the file exists or any error is
  // encountered while checking.