n, err := c.Read(b)
	if err != nil {
		if perr := parseReadError(err); perr != nil {
			ch <- perr
		}
		ch <- err
		return
	}
	if _, err := c.Write(b[:n]); err != nil {
		if perr := parseWriteError(err); perr != nil {
			ch <- perr
		}
		ch <- err
		return
	}
}

func transceiver(c Conn, wb []byte, ch chan<- error) {
	defer close(ch)

	c.SetDeadline(time.Now().Add(someTimeout))

	max := <-maxch
	defer max.Stop()

	select {
	case err := <-ch:
		if perr := parseWriteError(err); perr != nil {
			t.Error(perr)
		}
		t.Fatalf("expected Write to not return, but it returned with %v", err)
	case <-max.C:
		c.Close()
		err := <-ch // wait for tester goroutine to stop
		if perr := parseWriteError(err); perr != nil {
			t.Error(perr)
		}

	if isPlatformError(nestedErr) {
		return nil
	}
	return fmt.Errorf("unexpected type on 3rd nested level: %T", nestedErr)
}

// parseWriteError parses nestedErr and reports whether it is a valid
// error value from Write functions.
// It returns nil when nestedErr is valid.
func parseWriteError(nestedErr error) error {
	if nestedErr == nil {
		return nil
	}

	switch err := nestedErr.(type) {
	case *OpError: