You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: codec.go
    path of file: ./repos/cosmos-sdk/collections/colltest
    
    the code of the file until where you have to start completion: package colltest

import (
	"encoding/json"
	"fmt"
	"reflect"
	"testing"

	"github.com/stretchr/testify/require"

	"cosmossdk.io/collections"
	"cosmossdk
    
func (m mockValueCodec[T]) Decode(b []byte) (t T, err error) {
	wrappedValue := mockValueJSON{}
	err = json.Unmarshal(b, &wrappedValue)
	if err != nil {
		return
	}
	if !m.isInterface {
		err = json.Unmarshal(wrappedValue.Value, &t)
		return t, err
	}

	typ, exists := m.seenTypes[wrappedValue.TypeName]
	if !exists {
		return t, fmt.Errorf("unknown type %s, you're dealing with interfaces... in order to make the interface types known for the MockValueCodec, you need to first encode them", wrappedValue.TypeName)
	}

	newT := reflect.New(typ).Interface()
	err = json.Unmarshal(wrappedValue.Value, newT)
	if err != nil {
		return t, err
	}

	iface := new(T)
	reflect.ValueOf(iface).Elem().Set(reflect.ValueOf(newT).Elem())
	return *iface, nil
}