How to write a unit test for CronJob in Nestjs - unit-testing

Question

I am facing difficulty writing a unit test in jest for the code snippet below:
async addCronJob(props: IAddAndUpdateCronJobDetails) {
const {name, individualSchedule} = props;
const parsedCronTime = convertDateAndTimeToCron(
individualSchedule.timeOfRun,
individualSchedule.dateOfrun
)
const {jobType, dateOfRun, id, timeOfRun} = individualSchedule;
const newJob = new CronJob(
parsedCronTime,
async () => {
return this.sqsService.getSqsApproval({
//some properties
}).then(() => {
//some logic
})
},
null,
false,
'Asia/Singapore'
)
this.schedulerRegistry.addCronJob(name, newJob)
newJob.start()
}
And here is my unit test:
//at the top
jest.mock('cron', () => {
const mScheduleJob = {start: jest.fn(), stop: jest.fn()};
const mCronJob = jest.fn(() => mScheduleJob);
return {CronJob: mCronJob}
})
***************
describe('addCronJob', () => {
it('should add a new cron job', async (done) => {
const testFn = jest.fn();
const parsedCronTime = convertDateAndTimeToCron(
mockSchedule.timeOfRun,
mockSchedule.dateOfrun
)
const testCronJob = new CronJob(
parsedCronTime,
testFn,
null,
false,
'Asia/Singapore'
);
return dynamicCronService.addCron({//properties}).then(() => {
expect(CronJob).toHaveBeenCalledWith(//properties);
expect(testCronJob.start).toBeCalledTimes(1);
done()
})
})
})
The above test passes without error. However, it is unable to test for this block of async code within the cron job itself:
async () => {
return this.sqsService.getSqsApproval({
//some properties
}).then(() => {
//some logic
})
}
Anyone have an idea how to test the above block of code?
Thanks!

Answer 1

Probably late to the party, but I struggled with this myself and wanted to share my solution:
Method in service
async addCronJob(taskName: string, cronEx: string, onTickCallback: () => void | Promise<void>): Promise<void> {
const newJob = new CronJob(cronEx, onTickCallback);
this.schedulerRegistry.addCronJob(taskName, newJob);
newJob.start();
}
Test
it('should create cronJob', async () => {
await service.addCronJob(jobName, testCronExpression, callbackFunction);
expect(schedulerRegistryMock.addCronJob).toHaveBeenCalledWith(jobName, expect.any(CronJob));
jest.advanceTimersByTime(60 * 60 * 1000);
expect(callbackFunction).toHaveBeenCalled();
});
Instead of creating a test cronjob with a test function, I had to mock the actual function I'm expecting the cronjob to call on tick (in your case, that should be getSqsApproval I believe). Then I expected schedulerRegistry.addCronJob to be called with any CronJob, since I can't know the specific job. Creating a new job and expecting it here won't work.
Finally, I advanced the time by 1 hour because my testCronExpression was 0 * * * *. You should advance the time depending on the cron expression you use for testing.
Expecting the callbackFunction to have been called after the time passed (virtually) worked for me.
Hope this helps!