redux-saga-testing/jest/03.saga-with-data.spec.ts

A no-brainer way of testing your Sagas

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

interface ApiResult {
  id: number;
  title: string;
}

const api = jest.fn<string, []>();
const someAction = (payload: number[]) => ({ type: "SOME_ACTION", payload });

function* mySaga(): any {
  const someData = yield call(api);
  const transformedData = someData.map((x: ApiResult) => x.id);
  yield put(someAction(transformedData));
}

describe("When testing a Saga that manipulates data", () => {
  const it = sagaHelper(mySaga());

  it("should have called the mock API first, which returns some data", (result) => {
    expect(result).toEqual(call(api));
    return [
      { id: 1, title: "foo" },
      { id: 2, title: "bar" },
      { id: 3, title: "foobar" },
    ];
  });

  it("and then trigger an action with the transformed data we got from the API", (result) => {
    expect(result).toEqual(put(someAction([1, 2, 3])));
  });

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