Chapter 13 - Unit testing GraphQL

[Backend, Test]
Continues from branch chapter-12-solution

Note this chapter starts at the branch chapter-13 because we have to make a few changes before we can implement our test: Jest mocks don't work well with plain objects, so we moved the list-service to it's own file under pages/api/graphql/services/list-service.ts

In this chapter we're going to write unit test for our queries on the API side.

To unit test GraphQL APIs we use mocks using utilities provided by apollo, and the jest library.

We can write tests for our queries by using the execute function from graphql. The most basic test looks like this:

import gql from 'graphql-tag';
import { execute } from 'graphql/execution/execute';
import { makeExecutableSchema } from 'apollo-server-micro';
import { typeDefs } from '../schema';
import { resolvers } from '../resolvers';
import { ServiceUsedByResolver } from '../service-used-by-resolver';
jest.mock('../service-used-by-resolver');

describe('list query', () => {
    const schema = makeExecutableSchema({
        typeDefs,
        resolvers: {
            Query: resolvers.Query as any,
        },
    });

    it('calls list service', () => {
        execute({
            schema,
            variableValues: {
                search: 1,
            },
            document: gql`
                query myQuery($search: String!) {
                    myQuery(search: $search) {
                        id
                    }
                }
            `,
        });

        const mockCall = (ServiceUsedByResolver as any).mock.instances[0].single
            .mock.calls[0];
        expect(mockCall).toEqual([1]);
    });
});

Assignment 13.1: Implement a unit test

Modify the example above and implement a unit test on your own queries or mutations.

Chapter 13 - Solution

Branch chapter-13-solution

Assignment 13.1 - Solution: Implement a unit test

For our lists query we implement a unit test to check whether our service is correctly called

pages/api/graphql/test/list.query.test.ts

import gql from 'graphql-tag';
import { execute } from 'graphql/execution/execute';
import { makeExecutableSchema } from 'apollo-server-micro';
import { typeDefs } from '../schema';
import { resolvers } from '../resolvers';
import { ListService } from '../list-service';
jest.mock('../list-service');

describe('list query', () => {
    const schema = makeExecutableSchema({
        typeDefs,
        resolvers: {
            Query: resolvers.Query as any,
        },
    });

    it('calls list service', () => {
        execute({
            schema,
            variableValues: {
                id: 1,
            },
            document: gql`
                query list($id: Int!) {
                    list(id: $id) {
                        id
                    }
                }
            `,
        });

        const mockCall = (ListService as any).mock.instances[0].single.mock
            .calls[0];
        expect(mockCall).toEqual([1]);
    });
});