Constructing an error about rsocket-go HOT 6 CLOSED

package errors_test

import (
	"fmt"
	"log"
	"testing"

	"github.com/rsocket/rsocket-go"
)

type (
	ErrorCode uint32

	Error interface {
		rsocket.Error
	}
)

func (c ErrorCode) String() string {
	switch c {
	case ErrCodeMissingMetadata:
		return "MISSING_METADATA"
	default:
		return rsocket.ErrorCode(c).String()
	}
}
const (
	ErrCodeMissingMetadata ErrorCode = 0xA0000001
)

func New(code ErrorCode, data []byte) Error {
	return &customError{
		code: code,
		data: data,
	}
}

type customError struct {
	code ErrorCode
	data []byte
}

func (err *customError) Error() string {
	return fmt.Sprintf("%#x: %s", uint32(err.code), err.code)
}

func (err *customError) ErrorCode() rsocket.ErrorCode {
        // need to convert type, therefore losing `String()` implementation
	return rsocket.ErrorCode(err.code)
}

func (err *customError) ErrorData() []byte {
	return err.data
}

func TestCustomError(t *testing.T) {
	err := New(ErrCodeMissingMetadata, []byte("MyErrorData"))
	log.Println(err.Error())
	// logs "UNKNOWN"/ expected "MISSING_METADATA"
	log.Println(err.ErrorCode())
	log.Println(string(err.ErrorData()))
	// comparison is harder
	log.Println(ErrorCode(err.ErrorCode()) == ErrCodeMissingMetadata)
}

type customError struct {
	code ErrorCode
	data []byte
}

func (err customErr) Is(code ErrorCode) bool {
	return err.code == code
}