Proofread your Redux sagas. Saga testing tool.
npm install --save-dev proofread
A convenience method to decrease boilerplate when testing you Redux sagas with Jest. Consider you have a simple saga like this:
export function* saga() {
yield take('LOAD_USERS');
yield put(action());
}
Normally you would write tests for it like this:
it('standard saga testing', () => {
const iterator = saga();
expect(iterator.next().value).toEqual(take('LOAD_USERS'));
expect(iterator.next().value).toEqual(put(action()));
});
Notice how much boilerplate each like has and that basically the first
part of each line expect(iterator.next().value).toEqual(
is repeated.
proofread
let's you write saga tests without this boilerplate. This
is how you write the same test using the read
helper:
import {read} from 'proofread';
it('proofreading saga', () => {
read(saga, function* () {
yield take('LOAD_USERS');
yield put(action());
});
});
Here we "read" the saga and provide an alternative reading of it as a generator function. The real saga is matched step-by-step against the alternative reading and errors are thrown if any step of the reading does not match.
See /demo
folder for examples.
Each yield in the test generator returns a function. You can call that function with the value you want to be returned to your original saga:
(yield select(getSomething())(/* ... */);
Consider this saga:
export function* saga() {
yield take('AUTHENTICATE');
const isAuthenticated = yield select(getIsAuthenticated);
if(!isAuthenticated) {
yield put(action());
}
}
Normally you would write a test for it like this:
const iterator = saga();
expect(iterator.next().value).toEqual(take('AUTHENTICATE'));
expect(iterator.next().value).toEqual(select(getIsAuthenticated));
expect(iterator.next(false).value).toEqual(put(action()));
Notice how on the last line we supply the false
value for the yield select()
statement of the saga:
iterator.next(false).value
When proofreading this saga, you would do it like this:
read(saga, function* () {
yield take('AUTHENTICATE');
(yield select(getIsAuthenticated))(false);
yield put(action());
});
Here we provide the yielded value of the select
effect, like this:
(yield select(getIsAuthenticated))(false);
.
You would also want to test the saga when the if()
branch is failing,
conventionally you would do it like this:
const iterator = saga();
expect(iterator.next().value).toEqual(take('AUTHENTICATE'));
expect(iterator.next().value).toEqual(select(getIsAuthenticated));
expect(iterator.next(true).done).toEqual(true);
We fail the if-statement and test for the end of saga on the last like:
expect(iterator.next(true).done).toEqual(true);
When proofreading we would test for the branch fail like this:
read(saga, function* () {
yield take('AUTHENTICATE');
(yield select(getIsAuthenticated))(true);
return true;
});
This time the return true;
statements checks that the saga ended.
return true;
If you want to skip an effect in your saga, use __
:
import {__} from 'proofread';
read(saga, function* () {
yield __;
yield __;
yield take('SOME_ACTION');
});
The read
method returns a generator object:
let gen = read(saga, args);
So you can use it to test your sagas in conventional way as well, if you like:
expect(gen.next().value).toEqual(/* ... */);
At any point in time you can clone that generator. You will receive a new one at the same location in the saga:
let gen2 = gen.clone();
You can also use those generators to test your saga in proofreading way:
gen2.read(function* () {
yield put(someAction());
});
If saga throws an error, you can specify it by throwing an error in your
proofreading saga. To match any error, throw skip __
effect:
read(saga, function* () {
throw __;
});
Or specify the error more exactly by matching it:
read(saga, function* () {
throw new Error('message...');
});
Similarly, if your saga returns a value you can test it with a return statement, to match any return value:
read(saga, function* () {
return __;
});
Or you can specify an exact value the return statement has to match.
You can also use return __;
to check that saga has finished.
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