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: jsonpb_gogo_test.go
    path of file: ./repos/gitkube/vendor/github.com/gogo/protobuf/test/jsonpb-gogo
    
    the code of the file until where you have to start completion: package jsonpb_gogo

import (
	"testing"

	"github.com/gogo/protobuf/jsonpb"
)

// customFieldMessage implements protobuf.Message but is not a normal generated message type.
type customFieldMessage struc
    
func TestUnmarshalWithJSONPBUnmarshaler(t *testing.T) {
	rawJson := `{}`
	marshaler := &jsonpb.Marshaler{}
	msg := &customFieldMessage{someField: "Ignore me"}
	str, err := marshaler.MarshalToString(msg)
	if err != nil {
		t.Errorf("an unexpected error occurred when marshaling message: %v", err)
	}
	if str != rawJson {
		t.Errorf("marshaled JSON was incorrect: got %s, wanted %s", str, rawJson)
	}
}