Allow using `vi.mock` (and related) functions in tests

[MillerSvt]

Which @angular/* package(s) are relevant/related to the feature request?

core

Description

With the new Angular unit-test builder (Vite), test files are bundled into unified chunks.
Because of this full bundling step:

• ESM modules are statically linked at build time
• There is no runtime module graph available
• vi.mock() cannot intercept module loading
• Mocking entire modules (components/services/modules) is not possible

Currently if we use vi.mock function for automocking component/directives/services/pipes/etc..., we got an error:

Error: The "vi.mock" and related methods are not supported with the Angular unit-test system. Please use Angular TestBed for mocking.

TestBed overrides are insufficient because:

• They replace Angular metadata (providers/imports), not module implementation
• They cannot replace pure TS logic or side effects
• They do not intercept ESM import bindings

Proposed solution

Instead of runtime interception (like Vitest normally does), Angular test builder should:

1. Detect vi.mock() calls at compile time (in spec files, and in setupFiles)
2. Hoist them
3. Rewrite import bindings to use a generated mock registry
4. Replace module resolution during bundling

I suggest to create esbuild plugin, that:

1. Parse test file AST
2. Detect:

• vi.mock()
• vi.unmock()
• vi.doMock()
• vi.doUnmock()
• vi.importMock()
• vi.importActual()
• vi.hoisted()

3. Hoist mock calls
4. Rewrite imports

Example Transform Injectable

Before:

import { MyService } from './my-service';
import { MyOtherService } from './my-other-service';

vi.mock('./my-service', () => ({
  MyService:
    @Injectable({providedIn: 'root'})
    class {
      get() { return 'mock'; }
    }
}));

vi.mock('./my-other-service');

test(() => {
  const myService = new MyService();
  const myOtherService = new MyOtherService();
});

After:

// should initialize once in one environment
const __angularViMocks = (globalThis.__angular_vi_mocks ??= new Map<string, any>());

__angularViMocks.set(
  './my-service',
  (() => ({
    MyService: class {
      get() { return 'mock'; }
      static ɵprov = {
         providedIn: 'root',
         factory: () => new this();
      };
      static ɵfac = () => new this(); 
    }
  }))()
);

__angularViMocks.set(
  './my-other-service',
  (() => ({
    MyOtherService: class {
      get = vi.fn(); // maybe better to put `vi.fn()` to MyOtherService.prototype.get = vi.fn();
      static ɵprov = {
         providedIn: 'root',
         factory: () => new this();
      };
      static ɵfac = () => new this(); 
    }
  }))()
);

import * as __angularViActualMod1 from './my-service';
import * as __angularViActualMod2 from './my-other-service';

// We should replace that import in every dependent chunk.
const { MyService } = __angularViMocks.get('./my-service') ?? __angularViActualMod1;
const { MyOtherService } = __angularViMocks.get('./my-other-service') ?? __angularViActualMod2;

Requirements:

• Must mock full implementation (not only metadata) for any modules, as vi.mock() does
• Must stub components, services, modules, pipes, directives both metadata and implementation
• Must preserve ESM live bindings semantics
• Must preserve sourcemaps and coverage
• Must not require runtime module loader

Alternatives considered

Currently we have no choice, but stay with slow and inefficient jest + jest-preset-angular.

I've implemented deep-automocking infrastructure for jest.mock() ng-automocks-jest, it can stub any angular entities, both metadata and implementation.

[HerrDerb]

I did run into the same issue. I did mock an import (import { jwtDecode } from 'jwt-decode';) for test which now does not work anymore.

vi.mock('jwt-decode', () => ({
  jwtDecode: vi.fn(),
}));


it(...){
  //...
    (jwtDecode as ReturnType<typeof vi.fn>).mockReturnValue({
      realm_access: {
        roles: ['admin', 'user'],
      },
    });
  //...

}

[gcoadour]

Related to #31609

[MillerSvt]

@alan-agius4 let's continue here.

Instead TestBed.overrideProvider or TestBed.configureTestingModule should be used as is the supported way

TestBed is not enough to mocking. As described here, it cannot mock implementation. It can only override metadata. Also TestBed cannot mock platform providers, but only root providers.

If you want to stay framework agnostic, please allow us to add esbuild plugin to implement this thing by third-party plugin. We need to intercept vi.mock and related calls at compile-time, and transform it for tests bundle. I can create ng-automocks-vitest plugin and implement this mocks on my own.