Testing Your Subscriptions

Run it like a Function

Since subscriptions are just functions, you should easily be able to execute them. The signature of every subscription is (...params) => (dispatch) => cleanUpFn, so we know how to get the code to execute, and how to stop it, so what's preventing us from doing that? Let's take this subscription as an example:

mySubscription.js
export const mySubscription = (dispatch, delay, onIntervalAction) => dispatch => {
const handle = setInterval(dispatch, delay, onIntervalAction);
return () => {
clearInterval(handle);
};
};

Maybe a test could look something like this:

mySubscription.spec.js
import { mySubscription } from './mySubscription.js';
import * as sinon from 'sinon';
describe('mySubscription', () => {
it('creates an interval', () => {
expect.assertions(1);
sinon.spyOn(global, 'setInterval');
const dispatch = sinon.fake();
const myAction = () => {};
const cleanup = mySubscription(dispatch, 1000, myAction);
expect(global.setInterval.mock.calls).toHaveLength(1);
cleanup();
expect(dispatch.calledWith, [myAction]);
setInterval.restore();
});
});

End to End Testing

Calling your subscription in a test can get you fairly far, but the real test is when your application expects some sort of payload from your subscription.

myApplication.spec.js
import { app, effects } from 'ferp';
import { intervalSub } from './intervalSub.js';
const testify = (expectedActions, done) => (_, actionAnnotation) => {
const actionName = expectedActions.unshift();
expect(actionAnnotation).toBe(actionName);
if (expectedActions.length === 0) {
return done();
}
};
describe('myApplication', () => {
it('runs an effect from mySubscription', (done) => {
const myAction = state => [false, effects.none()];
app({
init: [true, effects.none()],
observe: testify([
'ferpAppInitialization', // this is just the action/annotation of `init`
'myAction',
], done),
subscribe: state => [
state && [intervalSub, 1000, myAction],
],
});
});
});