Dynamic Providers

You can use completely dynamic providers by passing in an object literal to the provide method. The object literal argument must contain effect creator names as keys and function handlers as values. Each function handler takes two arguments, the yielded effect and a next callback. You can inspect the effect and return a fake value based on the properties in the effect. If you don't want to handle the effect yourself, you can pass it on to Redux Saga by invoking the next callback parameter.

Here is an example with Jest to show you how to supply a fake value for an API call:

import { call, put, take } from 'redux-saga/effects';
import { expectSaga } from 'redux-saga-test-plan';
import api from 'my-api';

function* saga() {
  const action = yield take('REQUEST_USER');
  const id = action.payload;

  const user = yield call(api.fetchUser, id);

  yield put({ type: 'RECEIVE_USER', payload: user });
}

it('provides a value for the API call', () => {
  return expectSaga(saga)
    .provide({
      call(effect, next) {
        // Check for the API call to return fake value
        if (effect.fn === api.fetchUser) {
          const id = effect.args[0];
          return { id, name: 'John Doe' };
        }

        // Allow Redux Saga to handle other `call` effects
        return next();
      },
    })
    .put({
      type: 'RECEIVE_USER',
      payload: { id: 1, name: 'John Doe' },
    })
    .dispatch({ type: 'REQUEST_USER', payload: 1 })
    .run();
});

Effect Creators

Even though you'll probably never need them all, you can supply a provider for almost every effect creator*:

  • all **
  • actionChannel
  • call
  • cancel
  • cancelled
  • cps
  • flush
  • fork
  • join
  • put
  • race
  • select
  • spawn
  • take

*Because there is no way to distinguish the apply and call effects, you must handle apply effects with the call provider function.

*To handle take.maybe and put.resolve, use the take and put providers, respectively. You can inspect take effects for the maybe property and put effects for the resolve property.

** all will provide values for a yielded all effect as well as a yielded array. NOTE: yielding an array is deprecated in Redux Saga, so this functionality will be removed when Redux Saga removes support for yielded arrays.

Other Examples

Select

import { put, select } from 'redux-saga/effects';
import { expectSaga } from 'redux-saga-test-plan';
import { selectors } from 'my-selectors';

function* saga() {
  const name = yield select(selectors.getName);
  const age = yield select(selectors.getAge);

  yield put({ type: 'USER', payload: { name, age } });
}

it('provides a value for the selector', () => {
  return expectSaga(saga)
    .provide({
      select({ selector }, next) {
        if (selector === selectors.getName) {
          return 'Tucker';
        }

        if (selector === selectors.getAge) {
          return 11;
        }

        return next();
      },
    })
    .put({
      type: 'USER',
      payload: { name: 'Tucker', age: 11 },
    })
    .run();
});

Parallel Effects via all

Providers work on effects yielded inside an all effect.

import { all, put, select } from 'redux-saga/effects';
import { expectSaga } from 'redux-saga-test-plan';
import { selectors } from 'my-selectors';

function* saga() {
  const [name, age] = yield all([
    select(selectors.getName),
    select(selectors.getAge),
  ]);

  yield put({ type: 'USER', payload: { name, age } });
}

it('provides values for effects inside arrays', () => {
  return expectSaga(saga)
    .provide({
      select({ selector }, next) {
        if (selector === selectors.getName) {
          return 'Tucker';
        }

        if (selector === selectors.getAge) {
          return 11;
        }

        return next();
      },
    })
    .put({
      type: 'USER',
      payload: { name: 'Tucker', age: 11 },
    })
    .run();
});

Or you can provide a value for the entire array of effects via the all provider:

import { put, select } from 'redux-saga/effects';
import { expectSaga } from 'redux-saga-test-plan';
import { selectors } from 'my-selectors';

function* saga() {
  const [name, age] = yield [
    select(selectors.getName),
    select(selectors.getAge),
  ];

  yield put({ type: 'USER', payload: { name, age } });
}

it('provides a value for the entire array', () => {
  return expectSaga(saga)
    .provide({
      all: () => ['Tucker', 11],
    })
    .put({
      type: 'USER',
      payload: { name: 'Tucker', age: 11 },
    })
    .run();
});

Parallel Effects via an Array

Providers work on effects yielded inside an array. NOTE: yielding an array is deprecated in Redux Saga, so this functionality will be removed when Redux Saga removes support for yielded arrays.

import { put, select } from 'redux-saga/effects';
import { expectSaga } from 'redux-saga-test-plan';
import { selectors } from 'my-selectors';

function* saga() {
  const [name, age] = yield [
    select(selectors.getName),
    select(selectors.getAge),
  ];

  yield put({ type: 'USER', payload: { name, age } });
}

it('provides values for effects inside arrays', () => {
  return expectSaga(saga)
    .provide({
      select({ selector }, next) {
        if (selector === selectors.getName) {
          return 'Tucker';
        }

        if (selector === selectors.getAge) {
          return 11;
        }

        return next();
      },
    })
    .put({
      type: 'USER',
      payload: { name: 'Tucker', age: 11 },
    })
    .run();
});

Or you can provide a value for the entire array of effects via the all provider:

import { put, select } from 'redux-saga/effects';
import { expectSaga } from 'redux-saga-test-plan';
import { selectors } from 'my-selectors';

function* saga() {
  const [name, age] = yield [
    select(selectors.getName),
    select(selectors.getAge),
  ];

  yield put({ type: 'USER', payload: { name, age } });
}

it('provides a value for the entire array', () => {
  return expectSaga(saga)
    .provide({
      all: () => ['Tucker', 11],
    })
    .put({
      type: 'USER',
      payload: { name: 'Tucker', age: 11 },
    })
    .run();
});

Race

import { call, put, race, take } from 'redux-saga/effects';
import { expectSaga } from 'redux-saga-test-plan';
import api from 'my-api';

const delay = time => (
  new Promise(resolve => setTimeout(resolve, time))
);

function* saga() {
  const action = yield take('REQUEST_USER');
  const id = action.payload;

  const { user } = yield race({
    user: call(api.fetchUser, id),
    timeout: call(delay, 500),
  });

  if (user) {
    yield put({ type: 'RECEIVE_USER', payload: user });
  } else {
    yield put({ type: 'TIMEOUT' });
  }
}

test('fetching the user succeeds', () => {
  const fakeUser = { id: 1, name: 'John Doe' };

  return expectSaga(saga)
    .provide({
      race: () => ({ user: fakeUser }),
    })
    .put({ type: 'RECEIVE_USER', payload: fakeUser })
    .dispatch({ type: 'REQUEST_USER' })
    .run();
});

test('timeout wins', () => {
  return expectSaga(saga)
    .provide({
      race: () => ({ timeout: undefined }),
    })
    .put({ type: 'TIMEOUT' })
    .dispatch({ type: 'REQUEST_USER' })
    .run();
});

Errors

You can simulate errors by throwing from a provider:

function* saga() {
  const action = yield take('REQUEST_USER');
  const id = action.payload;

  try {
    const user = yield call(api.fetchUser, id);

    yield put({ type: 'RECEIVE_USER', payload: user });
  } catch (e) {
    yield put({ type: 'FAIL_USER', error: e });
  }
}

it('can throw errors in the saga', () => {
  const error = new Error('Whoops...');

  return expectSaga(saga)
    .provide({
      call(effect, next) {
        if (effect.fn === api.fetchUser) {
          throw error;
        }

        return next();
      },
    })
    .put({ error, type: 'FAIL_USER' })
    .dispatch({ type: 'REQUEST_USER', payload: 1 })
    .run();
});

Providing in Forked/Spawned Sagas

Providers work for effects in forked/spawned sagas too.

import { call, fork, put } from 'redux-saga/effects';
import { expectSaga } from 'redux-saga-test-plan';
import api from 'my-api';

function* fetchUserSaga() {
  const user = yield call(api.fetchUser);
  yield put({ type: 'RECEIVE_USER', payload: user });
}

function* forkingSaga() {
  yield fork(fetchUserSaga);
}

function* spawningSaga() {
  yield spawn(fetchUserSaga);
}

it('provides values in forked sagas', () => {
  return expectSaga(forkingSaga)
    .provide({
      call({ fn }, next) {
        if (fn === api.fetchUser) {
          return fakeUser;
        }

        return next();
      },
    })
    .put({ type: 'RECEIVE_USER', payload: fakeUser })
    .run();
});

it('provides values in spawned sagas', () => {
  return expectSaga(spawningSaga)
    .provide({
      call({ fn }, next) {
        if (fn === api.fetchUser) {
          return fakeUser;
        }

        return next();
      },
    })
    .put({ type: 'RECEIVE_USER', payload: fakeUser })
    .run();
});

Multiple Providers

You can supply multiple object providers via a couple methods. The easiest way is to pass in an array of object providers to the provide method. Provider functions will be composed according to the effect type, meaning the provider functions in the first object will be called before subsequent provider functions in the array.

Because provider functions are composed, they are similar to middleware. The next function argument inside provider functions allows you to delegate to the next provider in the middleware stack. If no more providers are available, then next will delegate to Redux Saga to handle the effect as normal.

import { call, put, select } from 'redux-saga/effects';
import api from 'my-api';
import * as selectors from 'my-selectors';

function* saga() {
  const user = yield call(api.findUser, 1);
  const dog = yield call(api.findDog);
  const greeting = yield call(api.findGreeting);
  const otherData = yield select(selectors.getOtherData);

  yield put({
    type: 'DONE',
    payload: { user, dog, greeting, otherData },
  });
}

const fakeUser = { name: 'John Doe' };
const fakeDog = { name: 'Tucker' };
const fakeOtherData = { foo: 'bar' };

const provideUser = ({ fn, args: [id] }, next) => (
  fn === api.findUser ? fakeUser : next()
);

const provideDog = ({ fn }, next) => (
  fn === api.findDog ? fakeDog : next()
);

const provideOtherData = ({ selector }, next) => (
  selector === selectors.getOtherData ? fakeOtherData : next()
);

it('takes multiple providers and composes them', () => {
  return expectSaga(saga)
    .provide([
      { call: provideUser, select: provideOtherData },
      { call: provideDog },
    ])
    .put({
      type: 'DONE',
      payload: {
        user: fakeUser,
        dog: fakeDog,
        greeting: 'hello',
        otherData: fakeOtherData,
      },
    })
    .run();
});

An alternative to supplying multiple provider objects is to only pass one object into provide and use the composeProviders function to compose multiple provider functions for a specific effect. You can import the composeProviders function from the redux-saga-test-plan/providers module. The provider functions are composed from left to right.

import { composeProviders } from 'redux-saga-test-plan/providers';

it('takes multiple providers and composes them', () => {
  return expectSaga(saga)
    .provide({
      call: composeProviders(
        provideUser,
        provideDog
      ),

      select: provideOtherData,
    })
    .put({
      type: 'DONE',
      payload: {
        user: fakeUser,
        dog: fakeDog,
        greeting: 'hello',
        otherData: fakeOtherData,
      },
    })
    .run();
});

More Examples

For some more contrived examples of providers, look in the repo tests.

Caveats

For providers to work, expectSaga will necessarily wrap forked/spawned sagas with an intermediary generator called sagaWrapper in order to intercept effects. To ensure that your saga receives back a task object with a correct name property, Redux Saga Test Plan will attempt to rename the sagaWrapper function to the name of a forked saga. This works in almost all JavaScript environments but will fail in PhantomJS. Therefore, you can't depend on the task name property being correct in PhantomJS.

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