I'm trying to write a test in nodeJS using Jest for a function that calls two async functions one after the other. I want to delay funcA, expect funcB to not be called, then run the timer down and expect funcB to be called.
The code looks something like this
//module1.js
async function mainFunc() {
await module2.funcA()
await module2.funcB()
}
//module2.js
async function funcA(){
// making some async operation
}
async function funcB(){
// making some async operation
}
I've tryed mocking the implementation of funcA like this:
const spyOnFuncA = jest.spyOn(module2, 'funcA').mockImplementation(async () => new Promise((r) => setTimeout(r, 1000)))
then in the test doing something like this:
test('Should not call second function until first function resolved', async () => {
jest.useFakeTimers()
const spyOnFuncA = jest.spyOn(module2, 'funcA').mockImplementation(async () => new Promise((r) => setTimeout(r, 1000)))
const spyOnFuncB = jest.spyOn(module2, 'funcB').mockImplementation()
mainFunc()
expect(spyOnFuncA).toBeCalled()
expect(spyOnFuncB).not.toBeCalled()
jest.runAllTimers()
expect(spyOnFuncB).toBeCalled()
})
I think the problem here is that the jest.useFakeTimers
contradicts with the setTimeout inside the mockImplementation
Any ideas how should I test this?
Would appreciate any idea
Cheers!
Mock funcA
to return a deferred promise, to be resolved later. I know sinon provides a promise helper to cover deferred so jest may include a similar construct. Otherwise here is one of the simple implementations from that answer:
class Deferred {
constructor() {
this.promise = new Promise((resolve, reject) => {
this.reject = reject
this.resolve = resolve
})
}
}
Then the mock is something like:
const deferred = new Deferred()
const spyOnFuncA = jest.spyOn(module2, 'funcA').mockImplementation(() => deferred.promise)
mainFunc() // avoid uncaught exceptions with `.catch`
.catch(err => expect(err).toBe(null))
expect(spyOnFuncA).toBeCalled()
expect(spyOnFuncB).not.toBeCalled()
await deferred.resolve('whatever')
expect(spyOnFuncB).toBeCalled()
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With