Jest spyOn HttpLink TypeError

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,
1

Hi,

I’ve written my own hook to implement a graphql client, but I’m having trouble with the types of HttpLink.

Here’s my hook:

import { setContext } from '@apollo/client/link/context';
import { ApolloClient, HttpLink, InMemoryCache } from '@apollo/client';

export function useGraphql() {

    const authLink = setContext((_, { headers }) => {
        return {
            headers: {
                ...headers,
            },
        };
    });

    const httpLink = new HttpLink({
        uri: 'https://example.com/graphql',
        credentials: 'include',
    });

    const client = new ApolloClient({
        cache: new InMemoryCache(),
        link: authLink.concat(httpLink),
    });
    return client;
}

Here’s the test:

import apollo, { HttpLink } from '@apollo/client';
import { useGraphql } from './use-graphql';
import 'whatwg-fetch';

jest.mock('@apollo/client', () => ({
    ...jest.requireActual('@apollo/client'),
}));


describe('useGraphql', () => {

    it('should return the Apollo client', async () => {

        const graphqlApi = 'http://example.com/graphql';

        const HttpLinkObject = {
            options: {
                uri: graphqlApi,
                credentials: "include"
            }
        };

        const client = useGraphql();

        jest.spyOn(HttpLink, HttpLinkObject)

        await expect(HttpLink).toHaveBeenCalledWith({
            uri: graphqlApi,
            credentials: 'include',
        });

        expect(ApolloClient).toHaveBeenCalledWith({
            cache: new InMemoryCache(),
            link: {},
        });

        expect(client).toBeInstanceOf(apollo.ApolloClient);
    });
});

The error that is tripping me up is

Type '{ options: { uri: string; credentials: string; }; }' is not assignable to type '"concat"'.
      Overload 2 of 4, '(object: typeof HttpLink, method: never): SpyInstance<never, never>', gave the following error.
        Argument of type '{ options: { uri: string; credentials: string; }; }' is not assignable to parameter of type 'never'.

A nudge in the right direction would be much appreciated!

2

For anyone coming across this, I was testing too much implementation detail. I settled for a test of the implementation itself, like this:

describe('useGraphql', () => {
    it('should return the Apollo client', async () => {
        const client = withGraphql();

        expect(client).toBeInstanceOf(apollo.ApolloClient);
    });
});

This still gave me 100% coverage.