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: example_test.go
    path of file: ./repos/asynq/x/rate
    
    the code of the file until where you have to start completion: package rate_test

import (
	"context"
	"fmt"
	"time"

	"github.com/hibiken/asynq"
	"github.com/hibiken/asynq/x/rate"
)

type RateLimitError struct {
	RetryIn time.Duration
}

func (e *RateLimitError) Error() string {
	return fmt.Sprintf("rate limited (retry in  %v)", e.RetryIn)
}

func ExampleNewSemaphore() {
	redisConnOpt := asynq.RedisClientOpt{Addr: ":6379"}
	sema := rate.NewSemaphore(redisConnOpt, "my_queue", 10)
	// call sema.Close() when appropriate

	_ = as
    
func ExampleNewSemaphore() {
	redisConnOpt := asynq.RedisClientOpt{Addr: ":6379"}
	sema := rate.NewSemaphore(redisConnOpt, "my_queue", 10)
	// call sema.Close() when appropriate

	_ = asynq.HandlerFunc(func(ctx context.Context, task *asynq.Task) error {
		ok, err := sema.Acquire(ctx)
		if err != nil {
			return err
		}
		if !ok {
			return &RateLimitError{RetryIn: 30 * time.Second}
		}

		// Make sure to release the token once we're done.
		defer sema.Release(ctx)

		// Process task
		return nil
	})
}