This program is not racy, but it's not deterministic either.

not-racy.go

package main

import (
	"fmt"
	"sync"
)

func main() {
	a := 0

	// This mutex protects variable a.
	var mu sync.Mutex

	// 2 tasks will be launched. The main goroutine will
	// wait for them to complete.
	var wg sync.WaitGroup
	wg.Add(2)

	go func() {
		mu.Lock()
		a = 22
		mu.Unlock()
		wg.Done()
	}()

	go func() {
		mu.Lock()
		a = 33
		mu.Unlock()
		wg.Done()
	}()

	wg.Wait()

	// It is possible that 22 is printed, or 33.
	fmt.Println(a)
}