toBeInstanceOf does not properly recognise instance when using baseUrl in tsconfig

[sosnowski]

Describe the bug

Hello All,

I've noticed unexpected behaviour that I believe is a bug. I've replicated it on Stackblitz, you can check it here: https://stackblitz.com/edit/node-qasnfa

As you can see, the tests fail on toBeInstanceOf check.

The tested function is very simple, it just creates an instance of the User class

import { User } from './user';

export const createDefaultUser = () => {
  return new User('DefaultName');
};

Now, this test fails, even though it should not:

import { createDefaultUser } from 'src/create';
import { User } from 'src/user';

describe('Test User class', () => {
  it('Should create user instance', () => {
    const u = createDefaultUser();
    expect(u).toBeInstanceOf(User);
  });
});

It fails, because create.ts file is importing user.ts "directly" ./user.ts, while the test suite is referrng to it in relation to tsconfig baseUrl setting.

If I change the import statement in the test suite...

import { createDefaultUser } from '../src/create';
import { User } from '../src/user';

describe('Test User class', () => {
  it('Should create user instance', () => {
    const u = createDefaultUser();
    expect(u).toBeInstanceOf(User);
  });
});

It works perfectly

Reproduction

https://stackblitz.com/edit/node-qasnfa

Just run npm run test

System Info

This is from Stacblitz but the same issue occurs on my MacOS

  System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 16.14.2 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 7.17.0 - /usr/local/bin/npm
  npmPackages:
    vitest: ^0.27.1 => 0.27.1

Used Package Manager

npm

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• The provided reproduction is a minimal reproducible example of the bug.

[sheremet-va]

Vitest doesn't recognise tsconfig. If you want to rely on it, install vite-tsconfig-paths plugin.

Your particular case incorrectly resolves url, but still loads a module, because it's relative to root. If you change baseUrl, it will still be loaded, even if TypeScript will give you the error. Your edge case should be resolved by #2687, but if you rely on tsconfig, you should install the plugin.

[sheremet-va]

This syntax is not supported without vite-tsconfig-paths. The fact that it "works" sometimes is a coincidence. When resolving paths, Vite thinks that src/user is relative to the current folder.