Testing InfiniteScroll component from react-infinite-scroller - reactjs

Question

I'm using react-infinite-scroller to make several calls to a paginated endpoint.
I haven't found any way to test the function that is triggered when a new request has to be done to the server.
I've taken a look at the github repository, but there is no information about how to trigger the function loadMore from a test.
The actual code looks like this:
<PaginatedList
data-testid="paginated-list-testid"
>
<InfiniteScroll
pageStart={0}
loadMore={this._nextPage}
hasMore={hasMore}
loader={<div key={0}>Loading...</div>}
useWindow={false}
>
{this._renderElements()}
</InfiniteScroll>
</PaginatedList>
The _nextPage function looks like follow:
async _nextPage() {
const { hasMore} = this.state;
const { externalCondition } = this.props;
if (hasMore) {
const response = externalCondition ? await this.repositoryA.next() : await this.repositoryB.next();
const nextElements = response.elements;
this.setState({
elements: nextElements,
loading: false,
hasMore: response.hasNext,
});
}
}
I wanna test that given an externalCondition the function this.repositoryA.next() is called. However, my test does not even reach this method.
This is my test:
test('Should\'ve called the repositoryA.next()', async () => {
const sampleUserId = 1;
const paginatedListTestId = "paginated-list-testid";
const renderComponent = render(
<PaginatedList
userId={sampleUserId}
/>,
);
const { getByTestId } = renderComponent;
fireEvent.scroll(getByTestId(paginatedListTestId), { target: { scrollY: 9000 } });
});
I know that my test does not have an assert yet, but I was debugging and I wasn't able to reach my function.
Neither scrolling to 9000 nor -9000.
Any help is welcome.
(The code has been a little bit changed due to privacy, so please, obviate any typo or mismatching variable names)