@swc/jest does not hoist mocks if the TypeScript file imports @jest/globals

[mogzol]

Problem

I have a TypeScript Jest test that imports jest from @jest/globals, and also mocks some modules. When compiled with swc, the mock is not hoisted to the top of the file like it should be. Removing the import for @jest/globals fixes the issue, but then Jest types don't work. Obviously that can be fixed by installing the @types/jest package instead of explicitly importing the globals, but I would expect either way to work, since Jest mentions both ways in it's documentation, and ts-jest supports both methods.

Reproduction

Say I have two files, example.ts, and its test, example.test.ts:

// example.ts
export function doSomething(): string {
  return "Module is NOT mocked!";
}

// example.test.ts
import { jest } from "@jest/globals";
import { doSomething } from "./example";

jest.mock("./example", () => ({
  doSomething: () => "Module is mocked!"
}))

test("mock works", () => {
  const result = doSomething();
  expect(result).toBe("Module is mocked!");
})

If I run Jest (configured to use @swc/jest) on the test, it fails because doSomething is imported from ./example before the mock is created. This can be seen by using the swc CLI with the same configuration that Jest uses:

> npx swc -C jsc.transform.hidden.jest=true -C module.type=commonjs example.test.ts

Outputs:

"use strict";
Object.defineProperty(exports, "__esModule", {
    value: true
});
var _globals = require("@jest/globals");
var _example = require("./example");
_globals.jest.mock("./example", function() {
    return {
        doSomething: function() {
            return "Module is mocked!";
        }
    };
});
test("mock works", function() {
    var result = (0, _example.doSomething)();
    expect(result).toBe("Module is mocked!");
});

Notice how the mock comes after the require statements.

Now, if I remove the @jest/globals import, and run Jest again, the test passes. Using the swc CLI we can see that the mock is properly hoisted to the top:

> npx swc -C jsc.transform.hidden.jest=true -C module.type=commonjs example.test.ts

"use strict";
jest.mock("./example", function() {
    return {
        doSomething: function() {
            return "Module is mocked!";
        }
    };
});
Object.defineProperty(exports, "__esModule", {
    value: true
});
var _example = require("./example");
test("mock works", function() {
    var result = (0, _example.doSomething)();
    expect(result).toBe("Module is mocked!");
});

Expected Behaviour

@swc/jest should work with TypeScript tests that explicitly import globals, the same way it works when the globals are implicit from @types/jest.

[jonaslalin]

One workaround to get the types from @jest/globals instead of @types/jest, is to add a jest-globals.d.ts file, and have that included in tsconfig.json:

import * as jestGlobals from '@jest/globals'
import type { ClassLike, FunctionLike, UnknownFunction } from 'jest-mock'

declare global {
  const expect: typeof jestGlobals.expect
  const it: typeof jestGlobals.it
  const test: typeof jestGlobals.test
  const fit: typeof jestGlobals.fit
  const xit: typeof jestGlobals.xit
  const xtest: typeof jestGlobals.xtest
  const describe: typeof jestGlobals.describe
  const xdescribe: typeof jestGlobals.xdescribe
  const fdescribe: typeof jestGlobals.fdescribe
  const beforeAll: typeof jestGlobals.beforeAll
  const beforeEach: typeof jestGlobals.beforeEach
  const afterEach: typeof jestGlobals.afterEach
  const afterAll: typeof jestGlobals.afterAll
  const jest: typeof jestGlobals.jest

  // biome-ignore lint/suspicious/noExplicitAny: fail function needs to accept any type to match Jest's implementation
  function fail(error?: any): never

  // biome-ignore lint/style/noNamespace: Namespace is required to match Jest's type system structure
  namespace jest {
    type Mock<T extends FunctionLike = UnknownFunction> = jestGlobals.jest.Mock<T>
    type Mocked<T extends object> = jestGlobals.jest.Mocked<T>
    type MockedClass<T extends ClassLike> = jestGlobals.jest.MockedClass<T>
    type MockedFunction<T extends FunctionLike> = jestGlobals.jest.MockedFunction<T>
    type MockedObject<T extends object> = jestGlobals.jest.MockedObject<T>
    type Replaced<T> = jestGlobals.jest.Replaced<T>
    type Spied<T extends ClassLike | FunctionLike> = jestGlobals.jest.Spied<T>
    type SpiedClass<T extends ClassLike> = jestGlobals.jest.SpiedClass<T>
    type SpiedFunction<T extends FunctionLike> = jestGlobals.jest.SpiedFunction<T>
    type SpiedGetter<T> = jestGlobals.jest.SpiedGetter<T>
    type SpiedSetter<T> = jestGlobals.jest.SpiedSetter<T>
  }
}

But the proper fix would be to fix the hoisting issue and explicit imports from @jest/globals