Invalid variable access: knex

[Ashwin]

Thank you for your work so far, this library looks like exactly what I need. However, when I try the example from the readme, I get an error:

The module factory of `jest.mock()` is not allowed to reference any out-of-scope variables. Invalid variable access: knex

Is there some configuration I'm missing? I can fix that error by using

jest.mock('../../knex', () => {
    const knex = require('knex');
    const mockKnexClient = require('knex-mock-client');
    return knex({ client: mockKnexClient.MockClient });
});

but then the next error appears:
TypeError: Class extends value undefined is not a constructor or null

What type of file does this library expect ../common/db-setup from the example to be? I tried export const db = knex(config); and export default knex(config); but that doesn't seem to be it.

[Felix Mosheev]

Thank you for opening this issue, I will fix the README example.

It depends on what your mocked module (in your case it is ../../knex) exports.

can you share it?

BTW, if your app gets its knex instance from "the outside" you can pass other instance (the one that will use knex-mock-client) in your tests.

[Ashwin]

This is my ../../knex/index.ts-file in full:

import config from '../knexfile.js';

/**
 * Global is used here to ensure the connection
 * is cached across hot-reloads in development
 *
 * see https://github.com/vercel/next.js/discussions/12229#discussioncomment-83372
 */
// @ts-expect-error TS2339: Property 'mysql' does not exist on type 'Global & typeof globalThis'.
let cached = global.mysql;
// @ts-expect-error TS2339: Property 'mysql' does not exist on type 'Global & typeof globalThis'.
if (!cached) cached = global.mysql = {};

export function getKnex() {
    if (!cached.instance) cached.instance = knex(config);
    return cached.instance;
}

export default knex(config);

I added the default export and tried using that export in both my code and tests, but it doesn't work. Thanks for your effort!

[Felix Mosheev]

I've just tested the README example,

import knex from 'knex';
import { getTracker } from '../dist';
import { MockClient } from '../dist';
import { db } from './db';

jest.mock('./db', () => {
  return { db: knex({ client: MockClient }) };
});

describe('jest mock', () => {
  it('should work', async () => {
    const tracker = getTracker();
    tracker.on.select('table_name').responseOnce([]);
    const response = await db.select('table_name');

    expect(response).toEqual([]);
  });
});

When ./db file is

// ./db.ts

import knex from 'knex';

export const db = knex({
  client: 'mysql',
});

And I don't get any of the errors you've mentioned.

[Felix Mosheev]

If your production code uses getKnex function, your jest.mock should mimic it.

it should look like:

jest.mock('../../knex/index', () => {
  return {
    getKnex: () => {
      return knex({ client: MockClient });
    },
  };
});

• It maybe an issue with the mocking path, if your app imports ../../knex (as nodejs allows to omit the index) you should specify the same way.

As per export default, jest docs specifies that you should mock it like this:

jest.mock('./esModule', () => ({
  __esModule: true, // <-- this property is important
  default: knex({ client: MockClient }),
}));

[Ashwin]

Yep, that's what I tried at first but that's when I get the Invalid variable access error. I changed it to:

jest.mock('../../knex/index.ts', () => {
    const knex = require('knex');
    return {
        getKnex: () => {
            return knex({ client: MockClient });
        },
    };
});

But that gives me the second error:

TypeError: Class extends value undefined is not a constructor or null
  at Object.<anonymous> (node_modules/knex-mock-client/dist/MockClient.js:9:41)

I'm really not sure what could cause this error. For the sake of completeness, my jest.config.js:

module.exports = {
    collectCoverageFrom: ['**/*.{js,jsx,ts,tsx}', '!**/*.d.ts', '!**/node_modules/**'],
    setupFilesAfterEnv: ['<rootDir>/setupTests.ts'],
    testPathIgnorePatterns: ['/node_modules/', '/.next/'],
    preset: 'ts-jest',
    testEnvironment: 'node',
};

package.json:

"ts-jest": "^26.5.6",
"jest": "^26.6.3",

[Felix Mosheev]

What is your knex version & node version?

[Ashwin]

I've tried version 0.95.4 to 0.95.6. Node is version 14.16.0.

[Felix Mosheev]

Weird, I'm using the same config.

Do you use TypeScript? if so, do you have "esModuleInterop": true, in your tsconfig.json?

[Ashwin]

Yes I have. Here is my full tsconfig.json:

{
    "ts-node": {
        "compilerOptions": {
            "module": "commonjs"
        }
    },
    "compilerOptions": {
        "target": "es5",
        "lib": ["dom", "dom.iterable", "esnext", "ESNext.Intl", "ES2018.Intl"],
        "allowJs": true,
        "skipLibCheck": true,
        "strict": false,
        "forceConsistentCasingInFileNames": true,
        "noEmit": true,
        "esModuleInterop": true,
        "module": "esnext",
        "moduleResolution": "node",
        "resolveJsonModule": true,
        "isolatedModules": true,
        "jsx": "preserve",
        "jsxImportSource": "@emotion/react",
        "typeRoots": ["types", "node_modules/@types"]
    },

    "include": ["**/*.ts", "**/*.tsx"],
    "exclude": ["node_modules"]
}

[Felix Mosheev]

From your error, looks like there is some issue with the default import of knex.

Can you put a console log in ./node_modules/knex-mock-client/dist/MockClient.js.

"use strict";
var __importDefault = (this && this.__importDefault) || function (mod) {
    return (mod && mod.__esModule) ? mod : { "default": mod };
};
Object.defineProperty(exports, "__esModule", { value: true });
exports.MockClient = void 0;
const knex_1 = __importDefault(require("knex"));
const Tracker_1 = require("./Tracker");

console.log(knex_1.default) // these 2
console.log(knex_1.default.Client)

class MockClient extends knex_1.default.Client {
...

or just prepare a small repo which will reproduce the bug

[Ashwin]

I've added the console.logs. knex itself is defined, however knex.Client is not.

 console.log
    [Function (anonymous)]

      at Object.<anonymous> (node_modules/knex-mock-client/dist/MockClient.js:11:9)

  console.log
    undefined

      at Object.<anonymous> (node_modules/knex-mock-client/dist/MockClient.js:12:9)

I'll setup a test repo to make things a bit easier to debug.

[Ashwin]

If I log knex_1.default(), as a function, I get the following result:

    {
      select: [Function: mockConstructor] {
        _isMockFunction: true,
        getMockImplementation: [Function (anonymous)],
        mock: [Getter/Setter],
        ...
      },
      from: [Function: mockConstructor] {
        _isMockFunction: true,
        getMockImplementation: [Function (anonymous)],
        mock: [Getter/Setter],
        ...
      },
      where: [Function: mockConstructor] {
        _isMockFunction: true,
        getMockImplementation: [Function (anonymous)],
        mock: [Getter/Setter],
        ...
      }
    }

[Felix Mosheev]

Ha, looks you have another global mock for knex :]

Maybe inside __mocks__

[Felix Mosheev]

Did you found the code that mocks knex?

[Ashwin]

Sorry, yes I did. I feel kinda stupid now, but it works :). It doesn't work with the getKnex-function, if I try to mock that I can't use the tracker. This isn't a big deal since I only need that in development. Thank you for your help!

[Felix Mosheev]

Glad to hear

if you have any feature requests / issues with the lib, I'll more than happy to help :]