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: workergroup_test.go
    path of file: ./repos/go-zero/core/threading
    
    the code of the file until where you have to start completion: package threading

import (
	"fmt"
	"runtime"
	"sync"
	"testing"

	"github.com/stretchr/testify/assert"
	"github.com/zeromicr
    
func TestWorkerGroup(t *testing.T) {
	m := make(map[string]lang.PlaceholderType)
	var lock sync.Mutex
	var wg sync.WaitGroup
	wg.Add(runtime.NumCPU())
	group := NewWorkerGroup(func() {
		lock.Lock()
		m[fmt.Sprint(RoutineId())] = lang.Placeholder
		lock.Unlock()
		wg.Done()
	}, runtime.NumCPU())
	go group.Start()
	wg.Wait()
	assert.Equal(t, runtime.NumCPU(), len(m))
}