| description |
|---|
Testing generator functions can get confusing when figuring out why a test is failing because the yielded value is actually yielding a different iteration. |
Use expect-to-yield to wrap your generator object with a helper function that keeps track of each iteration and provides the expectation function .toYieldValue(...) to assert the expected value. When a failure happens, get access to the iteration history to figure out what is going on.
Becoming a super hero is a fairly straight forward process:
$ npm install --save-dev expect-to-yield
import { iteratorWithHistory as i } from 'expect-to-yield';
function* counter() {
yield 1;
yield 2;
yield 3;
}
const itr = i(counter());// extend expect to have `.toYieldValue(...)
import 'expect-to-yield/extend-expect';
test('the iterator works', () => {
const itr = i(counter());
itr.next();
expect(itr).toYieldValue(1);
// // this fails the test and outputs:
// expected: 1
// received: 2
// history:
// > 1: 1
// 2: 2
// suggestion:
// expect(itr).toYieldValue(1);
});
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