Testing a scroll on an Animated.ScrollView - reactjs

Question

I am currently writing tests for a component I implemented using the react-test-renderer and an issue I've come across is trying to test the callback function that is called when I scroll on my Animated.ScrollView.
Here's a succint version of what I currently have with generic naming:
Component
export class MyComponent extends React.Component<MyComponentProps, MyComponentState> {
public componentWillMount() {
this.index = 0;
this.routeSelectionAnimation = new Animated.Value(0);
}
public componentDidMount() {
this.routeSelectionAnimation.addListener(({ value }) => {
// some work is done before the following line
// the function I want to test is being called
this.props.onIndexUpdate(index);
});
}
public render() {
const scrollAnimation = Animated.event(
[{
nativeEvent: {
contentOffset: {
x: this.routeSelectionAnimation,
},
},
},
],
{ useNativeDriver: true },
);
// * more processing *
return (
<Animated.ScrollView
horizontal={true}
scrollEventThrottle={1}
showsHorizontalScrollIndicator={false}
snapToInterval={...}
pagingEnabled={true}
onScroll={scrollAnimation} // what matters is this
style={styles.scrollView}
>
{other components}
</Animated.ScrollView>
);
}
This works correctly on the device, the function passed by props onIndexUpdate(int) is called when the ScrollView scrolls.
I would like to test this behaviour, however I can't seem to simulate the scroll on the ScrollView. I was thinking of doing something like:
const props = {
onIndexUpdate: jest.fn(),
};
const getTestInstance = () => {
return TestRenderer.create(
<MyComponent onIndexUpdate={props.onIndexUpdate} />
).root;
};
describe("Animated.ScrollView", () => {
it("calls function", () => {
const instance = getTestInstance();
const scrollView = instance.findByType(Animated.ScrollView);
scrollView.instance.scrollToEnd({animated: false});
expect(props.onIndexUpdate).toHaveBeenCalledTimes(3);
});
});
But it does not work. What I get as a result is TypeError: scrollView.instance.scrollToEnd is not a function which clearly shows I'm looking at this wrong...
I'd greatly appreciate input on how to fix this or approach the testing in a more correct way.

Answer 1

You missed out a print statement, thats why it wont work. You should have put:
print scrollView.instance.scrollToEnd({animated: false});