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: testsuite.go
    path of file: ./repos/go-toml/internal/testsuite
    
    the code of the file until where you have to start completion: // Package testsuite provides helper functions for interoperating with the
// language-agnostic TOML test suite at github.com/BurntSushi/toml-test.
package testsuite

import (
	"encoding/json"
	"fmt"
	"os"

	"github.com/pelletier/go-toml/v2"
)

// Marshal is a helpfer function for calling toml.Mars
    
func DecodeStdin() error {
	var decoded map[string]interface{}

	if err := toml.NewDecoder(os.Stdin).Decode(&decoded); err != nil {
		return fmt.Errorf("Error decoding TOML: %s", err)
	}

	j := json.NewEncoder(os.Stdout)
	j.SetIndent("", "  ")
	if err := j.Encode(addTag("", decoded)); err != nil {
		return fmt.Errorf("Error encoding JSON: %s", err)
	}

	return nil
}