redux-saga-testing/jest/06.saga-using-selectors.spec.ts

A no-brainer way of testing your Sagas

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

interface State {
  foo: string;
}

const loginAction = (payload: string) => ({ type: "LOGIN", payload });
const selectUsername = (state: State) => state.foo;

function* loginSaga(): any {
  const username = yield select(selectUsername);
  yield put(loginAction(username));
}

describe("When testing Saga that has a selector (fake login workflow)", () => {
  const it = sagaHelper(loginSaga());

  it("should select the current username from the state", (result) => {
    // Remember, we are not testing the selector here, just testing that the "select" function was called with a given selector function
    // The selector won't be executed (and it can't anyway, there is no state known to redux-saga on this test)
    expect(result).toEqual(select(selectUsername));
    // We return what the selector should have returned
    return "donald.drumpf";
  });

  it("should trigger the login action with the username we got from the state", (result) => {
    expect(result).toEqual(put(loginAction("donald.drumpf")));
  });

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