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: tester_test.go
    path of file: ./repos/goka/tester
    
    the code of the file until where you have to start completion: package tester

import (
	"testing"

	"github.com/lovoo/goka"
	"github.com/lovoo/goka/codec"
	"github.com/stretchr/testify/require"
)

type failingT struct {
	failed bool
}

func (ft *failingT) Errorf(format string, args .
    
func TestTester(t *testing.T) {
	var ft failingT
	gkt := New(&ft)

	goka.NewProcessor(nil,
		goka.DefineGroup("", goka.Input("input", new(codec.Int64), func(ctx goka.Context, msg interface{}) {})),
		goka.WithTester(gkt))

	// make sure that an invalid group graph fails the test
	require.True(t, ft.failed)
}