What's the best way to test redux-saga's `all` effect? - testing

Question

I have a saga which currently has a yield all(...) and I'm trying to figure out how to test to see that I'm actually invoking all() with the correct functions. Here's a stripped-down version of what I'm working with:
function* start() {
// I'd prefer not to start the status polling and the listening for
// the cancellation until after the request has been submitted, but
// I'm having trouble figuring out how to do that. So I'm just going
// to listen for 'em all up front here until I'm smarter.
yield all([
waitForCreateRequest(),
waitForPollStatus(),
waitForCancelRequest(),
])
}
function* waitForCreateRequest() {
while ( true ) {
try {
const { payload } = yield take('CREATE_REQUEST')
// ...
} catch ( error ) {
// ...
}
}
}
function* waitForPollStatus() {
while ( true ) {
try {
const { payload } = yield take('POLL_STATUS')
// ...
} catch ( error ) {
// ...
}
}
}
function* waitForCancelRequest() {
while ( true ) {
try {
yield take('CANCEL_REQUEST')
// ...
} catch ( error ) {
// ...
}
}
}
The test that I wrote (using Mocha and bdd-lazy-var) goes something like this:
describe('MySaga', () => {
describe('*start()', () => {
subject(start())
it('calls `all()` with the correct functions', () => {
expect($subject.next().value).to.eql(all([
waitForSubmitExportRequest(),
waitForPollExportStatus(),
waitForCancelExportRequest(),
]))
})
})
})
There is no output--it just hangs...and then I get a "JavaScript heap out of memory" error.
If I console.log($subject.next().value) instead:
describe('MySaga', () => {
describe('*start()', () => {
subject(start())
it.only('foo', () => {
console.log($subject.next().value)
})
})
})
This is what I get:
MySaga
*start()
{ '##redux-saga/IO': true,
ALL:
[ GeneratorFunctionPrototype { _invoke: [Function: invoke] },
GeneratorFunctionPrototype { _invoke: [Function: invoke] },
GeneratorFunctionPrototype { _invoke: [Function: invoke] } ] }
✓ foo
So I'm not sure what's going on here.
Countless Google searches didn't really turn up anything useful, and the closest SO post that I found (how to test redux-saga all effect using jest) was also unhelpful.

Answer 1

Is it a typo that your start function is not a generator function?
Anyway. Can you try to rewrite your start function like this:
function* start() {
yield all([
call(waitForCreateRequest),
call(waitForPollStatus),
call(waitForCancelRequest),
])
}
Now your test could look like:
it('calls `all()` with the correct functions', () => {
expect($subject.next().value).to.eql(all([
call(waitForSubmitExportRequest),
call(waitForPollExportStatus),
call(waitForCancelExportRequest),
]))
})