How to test redux-saga take with pattern function by Jest? - unit-testing

Question

I have some saga using take effect to get action by pattern. Now, I'm trying to test it:
Saga:
export function* mySaga(spaceId) {
while (true) {
const action = yield take(
action =>
action.type === MEDIA_SESSION_RESPONSE &&
action.payload.data.category === ScreenShareData &&
action.payload.data.topicId === spaceId
);
const remoteScreenSessionId = action.payload.data.content.sessionId;
yield put(addRemoteScreenSessionId(remoteScreenSessionId));
}
}
Test:
it('test', () => {
const gen = sagas.mySaga('space_1');
expect(gen.next().value).toEqual(
take(
action =>
action.type === MEDIA_SESSION_RESPONSE &&
action.payload.data.category === ScreenShareData &&
action.payload.data.topicId === spaceId
)
);
});
In take pattern I have an anonymous function, so how I can to test that pattern in take is equals to pattern, I provide in test?
Test result now is:
Expected value to equal:
{"##redux-saga/IO": true, "combinator": false, "payload": {"pattern": [Function anonymous]}, "type": "TAKE"}
Received:
{"##redux-saga/IO": true, "combinator": false, "payload": {"pattern": [Function anonymous]}, "type": "TAKE"}
If I will use JSON.stringify, I can't be sure that patterns are equal.

Answer 1

Jest can help you assert on the order of effects layer. In unit testing, you want to test a snippet of code (i.e saga, function, etc) not a flow of execution chain. Hence, the pattern you are trying to test is given [Function anonymous].
There is a little library called k-redux-saga-tester that can provide you with the flexibility of asserting on patterns. Fill in the VALUEs and create the necessary mocks for MEDIA_SESSION_RESPONSE, ScreenShareData, spaceId. It should look something like this:
describe('mySaga', () => {
describe('search', () => {
const test = tester(mySaga) <--- your saga
const spaceId = 'VALUE';
const MEDIA_SESSION_RESPONSE = 'VALUE';
const ScreenShareData = 'VALUE';
const payload = { data: { category: VALUE, topicId: VALUE }};
const action = { type: 'YOUR_ACTION_TYPE', payload: { payload }};
it('should search and set something', () => {
const mocks = {
take: [action =>
action.type === MEDIA_SESSION_RESPONSE &&
action.payload.data.category === ScreenShareData &&
action.payload.data.topicId === spaceId]
}
expect(test(mocks)).toMatchSnapshot()
})
})
})
In general, if you want to test the pattern, use a separate test for testing only that specific function. And assert it output given different arguments.