test saga try and catch

api.js

const api = {
  fetchProductAPI() {
    return 'iphone';
  },
};
export default api;

saga.js

import { call, put } from 'redux-saga/effects';
import api from './api';

export default function* fetchProduct() {
  try {
    yield call(api.fetchProductAPI);
    yield put({ type: 'PRODUCTS_RECEIVED', product: 'iphone' });
  } catch (error) {
    yield put({ type: 'PRODUCTS_REQUEST_FAILED', error });
  }
}

saga.test.js

/* eslint-disable redux-saga/yield-effects */

import { put, call } from 'redux-saga/effects';
import fetchProduct from './saga';
import api from './api';

describe('fetchProduct()', () => {
  it('try', () => {
    const gen = fetchProduct();
    expect(gen.next().value).toEqual(call(api.fetchProductAPI));
    expect(gen.next().value).toEqual(put({ type: 'PRODUCTS_RECEIVED', product: 'iphone' }));
  });
  it('catch', () => {
    const error = 'product not found';
    const gen = fetchProduct();
    
    gen.next(); // <== before throw error, you need to execute gen.next();
    
    expect(gen.throw('product not found').value).toEqual(put({ type: 'PRODUCTS_REQUEST_FAILED', error }));
  });
});