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Allow using vi.mock (and related) functions in tests #32641

@MillerSvt

Description

@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()
  1. Hoist mock calls
  2. 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.

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