Testing and mocking fetch in async useEffect and async Redux-Saga - jestjs

Question

I'm testing a functional component, that use React-Hooks and Redux-Saga. I can pass parameters in URL for the component, because they are a login page component.
My URL i pass is 'localhost/access/parameter', and when this parameter exists, i need to call a async redux saga, and if the fetch is OK, i put the result in redux-store. When the result is on redux-store, i have a useEffect that verify the result and if is OK, i put her in a input.
I can mock the result with axios, but i'm migrating to use only fetch. i mock the fetch, but when i use
mount(component), provided by enzyme, i do not how to await the redux-saga termine the request and useEffect do your job. I put a console log inside a effect, saga and log the input props to see your value prop, but the value is always empty . I tried to use setImmediate() and process.nextTick().
Links i use to write the code: 1,2, 3
I'm using formik, so they pass some props to me.
My component
const Login = ({
setFieldError, errors, response, fetchDomain, location, values, handleChange, handleBlur, setFieldValue, history,
}) => {
useEffect(() => {
async function fetchUrlDomain() {
const { pathname } = location;
const [, , domain] = pathname.split('/');
if (typeof domain !== 'undefined') {
await fetchDomain(domain);
}
}
fetchUrlDomain();
}, [fetchDomain, location]);
useEffect(() => {
if (typeof response === 'string') {
setFieldError('domain', 'Domain not found');
inputDomain.current.focus();
} else if (Object.keys(response).length > 0) {
setFieldValue('domain', response.Domain);
setFieldError('domain', '');
}
}, [response, setFieldValue, setFieldError]);
return (
<input name="domain" id="domain" value={values.domain} onChange={handleChange} onBlur={handleBlur} type="text" />
);
}
const LoginFormik = withFormik({
mapPropsToValues: () => ({ domain: '' }),
enableReinitialize: false,
validateOnBlur: false,
validateOnChange: false,
})(Login);
const mapStateToProps = () => ({ });
const mapDispatchToProps = dispatch => ({
fetchDomain: (value) => {
dispatch(action({}, constants.RESET_RESPONSE_DOMAIN));
dispatch(action(value, constants.FETCH_DOMAIN_REQUEST));
},
});
export default connect(mapStateToProps, mapDispatchToProps)(LoginFormik);
My Saga
export function* fetchDomain(action) {
const url = yield `${mainUrl}/${action.payload}`;
try {
const response = yield fetch(url).then(res => res.json());
yield put(reduxAction(response , constants.FETCH_DOMAIN_SUCCESS));
} catch (e) {
yield put(reduxAction(e, constants.FETCH_DOMAIN_FAILURE));
}
}
My Reducer
case constants.FETCH_DOMAIN_FAILURE:
return { ...initialState, response: 'Domain not found' };
case constants.FETCH_DOMAIN_SUCCESS: {
const { payload } = action;
return {
...initialState,
id: payload.Id,
apis: payload.Apis,
response: payload,
};
}
case constants.RESET_RESPONSE_DOMAIN:
return { ...initialState };
My Test
it('input with fetch only', (done) => {
const mockSuccessResponse = {
Id: 'fafafafa',
Apis: [],
Domain: 'NAME',
};
const mockJsonPromise = Promise.resolve(mockSuccessResponse);
const mockFetchPromise = Promise.resolve({
json: () => mockJsonPromise,
});
global.fetch = jest.fn().mockImplementation(() => mockFetchPromise);
const wrapper = mount(
<Provider store={store}>
<LoginForm
history={{ push: jest.fn() }}
location={{ pathname: 'localhost/login/Domain' }}
/>
</Provider>,
);
process.nextTick(() => {
const input = wrapper.find('#domain');
console.log(input.props());
expect(input.props().value.toLowerCase()).toBe('name');
global.fetch.mockClear();
done();
});
});
I expect my input have value, but he don't. I tried to use jest-fetch-mock but just don't work, and i want to use native jest methods, no thirty party libraries.

Answer 1

I cannot say what's wrong with your current code. But want to propose different approach instead.
Currently you are testing both redux part and component's one. It contradicts with unit testing strategy when ideally you should mock everything except module under the test.
So I mean if you focus on testing component itself it'd be way easier(less mocks to create) and more readable. For that you need additionally export unwrapped component(Login in your case). Then you can test only its props-vs-render result:
it('calls fetchDomain() with domain part of location', () => {
const fetchDomain = jest.fn();
const location = { pathName: 'example.com/path/sub' }
shallow(<Login fetchDomain={fetchDomain} location={location} />);
expect(fetchDomain).toHaveBeenCalledTimes(1);
expect(fetchDomain).toHaveBeenCalledWith('example.com');
});
it('re-calls fetchDomain() on each change of location prop', () => {
const fetchDomain = jest.fn();
const location = { pathName: 'example.com/path/sub' }
const wrapper = shallow(<Login fetchDomain={fetchDomain} location={location} />);
fetchDomain.mockClear();
wrapper.setProps({ location: { pathName: 'another.org/path' } });
expect(fetchDomain).toHaveBeenCalledTimes(1);
expect(fetchDomain).toHaveBeenCalledWith('another.org');
});
And the same for other cases. See with this approach if you replace redux with direct call to fetch() or whatever, or if you refactor that data to come from parent instead of reading from redux store you will not need to rewrite tests removing mocks to redux. Sure, you will still need to test redux part but it also can be done in isolation.
PS and there is no profit to await fetchDomain(...) in useEffect since you don't use what it returns. await does not work like a pause and that code may rather confuse reader.