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Current behavior

Real issue in my code, explanation, workaround and root cause created with the help of an IA.

Since @suites/unit@3.1.0 and @suites/doubles.jest@3.1.0, projects compiling with skipLibCheck: false fail with TS2300 Duplicate identifier 'Stub' and TS2300 Duplicate identifier 'Mocked'. @suites/unit@3.0.1 works fine.

The cause is that @suites/unit 3.1.0 now exports Stub and Mocked directly from its barrel, while @suites/doubles.jest 3.1.0 still augments the @suites/unit module with the same identifiers via declare module '@suites/unit'. The same names are therefore declared twice in the same module.

Root cause

node_modules/@suites/unit/dist/esm/index.d.ts in 3.1.0:

/// <reference types="@suites/doubles.jest/unit" />
export { TestBed } from './testbed.js';
export type { UnitTestBed, TestBedBuilder, Mocked, SolitaryTestBedBuilder, SociableTestBedBuilder, } from './types.js';
export type { UnitReference, MockOverride } from '@suites/core.unit';
export type { Stub } from '@suites/types.doubles';

node_modules/@suites/doubles.jest/unit.d.ts in 3.1.0 (kept from 3.0.x):

declare module '@suites/unit' {
  export type Stub<TArgs extends any[] = any[]> = JestStub<TArgs>;
  export type Mocked<T> = JestMocked<T>;
  // ...
}

Stub and Mocked are now declared twice in the @suites/unit module — once via direct export, once via module augmentation — which TypeScript reports as a duplicate identifier when lib-check is on.

In 3.0.1, @suites/unit/index.d.ts did not export Stub/Mocked; the only source was the augmentation in @suites/doubles.jest. No conflict.

Suggested fix

Either:

• (a) drop the direct exports of Stub and Mocked from @suites/unit/index.d.ts (revert to the 3.0.x layout where adapters own these types via augmentation), or
• (b) drop the declare module '@suites/unit' { export type Stub … } block from each adapter (@suites/doubles.jest, @suites/doubles.sinon, @suites/doubles.vitest, …) and let @suites/unit own them.

Option (b) is probably preferred since Mocked is already exported from @suites/unit/types.js directly.

Workaround

Pin to 3.0.1 with a ~ range in package.json:

"@suites/unit": "~3.0.1",
"@suites/doubles.jest": "~3.0.1",
"@suites/di.nestjs": "~3.0.1"

Environment

• TypeScript: 5.9.3
• Node: 22.x
• OS: Linux
• tsconfig: skipLibCheck: false, strict: false

Minimum reproduction code

https://github.com/ghislain-sn/suites-issue-types/

Steps to reproduce

mkdir suites-repro && cd suites-repro
npm init -y
npm i -D typescript @suites/unit@3.1.0 @suites/doubles.jest@3.1.0 @suites/di.nestjs@3.1.0 jest @types/jest

tsconfig.json:

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "strict": false,
    "skipLibCheck": false
  },
  "include": ["src"]
}

src/index.ts:

import { TestBed } from '@suites/unit'
export { TestBed }

$ npx tsc --noEmit
node_modules/@suites/doubles.jest/unit.d.ts:21:15 - error TS2300: Duplicate identifier 'Stub'.

21   export type Stub<TArgs extends any[] = any[]> = JestStub<TArgs>;
                 ~~~~

  node_modules/@suites/unit/dist/esm/index.d.ts:5:15
    5 export type { Stub } from '@suites/types.doubles';
                    ~~~~
    'Stub' was also declared here.

node_modules/@suites/doubles.jest/unit.d.ts:39:15 - error TS2300: Duplicate identifier 'Mocked'.

39   export type Mocked<T> = JestMocked<T>;
                 ~~~~~~

  node_modules/@suites/unit/dist/esm/index.d.ts:3:44
    3 export type { UnitTestBed, TestBedBuilder, Mocked, SolitaryTestBedBuilder, SociableTestBedBuilder, } from './types.js';
                                                 ~~~~~~
    'Mocked' was also declared here.

node_modules/@suites/unit/dist/esm/index.d.ts:3:44 - error TS2300: Duplicate identifier 'Mocked'.

3 export type { UnitTestBed, TestBedBuilder, Mocked, SolitaryTestBedBuilder, SociableTestBedBuilder, } from './types.js';
                                             ~~~~~~

  node_modules/@suites/doubles.jest/unit.d.ts:39:15
    39   export type Mocked<T> = JestMocked<T>;
                     ~~~~~~
    'Mocked' was also declared here.

node_modules/@suites/unit/dist/esm/index.d.ts:5:15 - error TS2300: Duplicate identifier 'Stub'.

5 export type { Stub } from '@suites/types.doubles';
                ~~~~

  node_modules/@suites/doubles.jest/unit.d.ts:21:15
    21   export type Stub<TArgs extends any[] = any[]> = JestStub<TArgs>;
                     ~~~~
    'Stub' was also declared here.


Found 4 errors in 2 files.

Errors  Files
     2  node_modules/@suites/doubles.jest/unit.d.ts:21
     2  node_modules/@suites/unit/dist/esm/index.d.ts:3

Expected behavior

npx tsc --noEmit exits 0 (as it does on 3.0.1).

Suites version

3.1.0

Node.js version

22.22.0

In which operating systems have you tested?

• macOS
• Windows
• Linux

Other

No response