redux-saga-testing/jest/02.simple-saga.spec.ts

A no-brainer way of testing your Sagas

import sagaHelper from "../helper";
import { call, put } from "redux-saga/effects";
import "jest";

const api = jest.fn();
const someAction = () => ({ type: "SOME_ACTION", payload: "foo" });

function* mySaga() {
  yield call(api);
  yield put(someAction());
}

describe("When testing a very simple Saga", () => {
  const it = sagaHelper(mySaga());

  it("should have called the mock API first", result => {
    // Here we test that the generator did run the "call" function, with the "api" as an argument.
    // The api funtion is NOT called.
    expect(result).toEqual(call(api));

    // It's very important to understand that the generator ran the 'call' function,
    // which only describes what it does, and that the API itself is never called.
    // This is what we are testing here: (but you don't need to test that in your own tests)
    expect(api).not.toHaveBeenCalled();
  });

  it("and then trigger an action", result => {
    // We then test that on the next step some action is called
    // Here, obviously, 'someAction' is called but it doesn't have any effect
    // since it only returns an object describing the action
    expect(result).toEqual(put(someAction()));
  });

  it("and then nothing", result => {
    expect(result).toBeUndefined();
  });
});