How to test take(function)?

[denchen]

If I have this relatively simple saga:

export function* test() {
  yield take(action =>
    action.type === 'FOO' && action.key === 'mykey'
  );
  // Some more logic
}

How would I go about unit-testing this? The examples I've seen with take() all assume a string, not a function.

[jfairbank]

Hi, @denchen.

You can test this a couple ways, depending on if you're using testSaga or expectSaga. With testSaga, you can use the inspect method to get the take effect. Then, you can unwrap it to get your selectAction function and make sure it passes with an expected action. You can do something similar with the provide method of expectSaga. I added the return for an example of additional logic, but you do whatever. Notice that I used next(42) in testSaga after the inspect call and that I return 42 in the provider for expectSaga.

import { asEffect } from 'redux-saga/utils';
import { take } from 'redux-saga/effects';
import { testSaga, expectSaga } from '../src';

function* test() {
  const value = yield take(action =>
    action.type === 'FOO' && action.key === 'mykey'
  );

  return value;
}

it('testSaga test', () => {
  const action = { type: 'FOO', key: 'mykey' };

  testSaga(test)
    .next()
    .inspect((effect) => {
      const selectAction = asEffect.take(effect).pattern;
      expect(selectAction(action)).toBe(true);
    })
    .next(42)
    .returns(42);
});

it('expectSaga test', () => {
  const action = { type: 'FOO', key: 'mykey' };

  return expectSaga(test)
    .provide({
      take(takeEffect) {
        const selectAction = takeEffect.pattern;
        expect(selectAction(action)).toBe(true);
        return 42;
      },
    })
    .returns(42)
    .run();
});

[jfairbank]

Closing this for now. Let me know if you have any other questions @denchen.

[yelworc]

Just had the same question and this example helped me a lot – might be a good addition to the Dynamic Providers documentation :)