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_cron_job_test.go
    path of file: ./repos/river
    
    the code of the file until where you have to start completion: package river_test

import (
	"context"
	"fmt"
	"log/slog"

	"github.com/jackc/pgx/v5/pgxpool"
	"github.com/robfig/cron/v3"

	"github.com/riverqueue/river"
	"github.com/riverqueue/river/internal/riverinternaltest"
	"github.com/riverqueue/river/internal/util/slogutil"
	"github.com/riverqueue/river/riverdriver/riverpgxv5"
)

type CronJobArgs struct{}

// Kind is the unique string name for this job.
func (CronJobArgs) Kind() string { return "cron" }

// CronJobWorker is a job worker for sorting strings.
type CronJobWorker struct {
	river.WorkerDefaults[CronJobArgs]
}

func (w *CronJobWorker) Work(ctx context.Context, job *river.Job[CronJobArgs]) error {
	fmt.Printf("This job will run once immediately then every hour on the half hour\n")
	return nil
}

// Example_cronJob demonstrates how to create a cron job with a more complex
// schedule using a third party cron package to parse more elaborate crontab
// syntax.
func Example_cronJob() {
	ctx := context.Background()

	dbPool, err := pgxpool.NewWithConfig(ctx, riverinternaltest.DatabaseConfig("river_testdb_example"))
	if err
    
func Example_cronJob() {
	ctx := context.Background()

	dbPool, err := pgxpool.NewWithConfig(ctx, riverinternaltest.DatabaseConfig("river_testdb_example"))
	if err != nil {
		panic(err)
	}
	defer dbPool.Close()

	// Required for the purpose of this test, but not necessary in real usage.
	if err := riverinternaltest.TruncateRiverTables(ctx, dbPool); err != nil {
		panic(err)
	}

	workers := river.NewWorkers()
	river.AddWorker(workers, &CronJobWorker{})

	schedule, err := cron.ParseStandard("30 * * * *") // every hour on the half hour
	if err != nil {
		panic(err)
	}

	riverClient, err := river.NewClient(riverpgxv5.New(dbPool), &river.Config{
		Logger: slog.New(&slogutil.SlogMessageOnlyHandler{Level: slog.LevelWarn}),
		PeriodicJobs: []*river.PeriodicJob{
			river.NewPeriodicJob(
				schedule,
				func() (river.JobArgs, *river.InsertOpts) {
					return CronJobArgs{}, nil
				},
				&river.PeriodicJobOpts{RunOnStart: true},
			),
		},
		Queues: map[string]river.QueueConfig{
			river.QueueDefault: {MaxWorkers: 100},
		},
		Workers: workers,
	})
	if err != nil {
		panic(err)
	}

	// Out of example scope, but used to wait until a job is worked.
	subscribeChan, subscribeCancel := riverClient.Subscribe(river.EventKindJobCompleted)
	defer subscribeCancel()

	// There's no need to explicitly insert a periodic job. One will be inserted
	// (and worked soon after) as the client starts up.
	if err := riverClient.Start(ctx); err != nil {
		panic(err)
	}

	waitForNJobs(subscribeChan, 1)

	if err := riverClient.Stop(ctx); err != nil {
		panic(err)
	}

	// Output:
	// This job will run once immediately then every hour on the half hour
}