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: defer_test.go
    path of file: ./repos/under-the-hood/demo/ch09lang/defer
    
    the code of the file until where you have to start completion: package main_test

import (
	"sync"
	"testing"
)

var lock sync.Mutex

func No
    
func foo(x int) int {
	// fast path
	if x != 42 {
		return x
	}
	// slow path
	mu.Lock()
	defer mu.Unlock()
	seq++
	return seq
}