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Allow using vi.mock (and related) functions in tests #32641
Description
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:
- Detect
vi.mock()calls at compile time (in spec files, and in setupFiles) - Hoist them
- Rewrite import bindings to use a generated mock registry
- Replace module resolution during bundling
I suggest to create esbuild plugin, that:
- Parse test file AST
- Detect:
vi.mock()vi.unmock()vi.doMock()vi.doUnmock()vi.importMock()vi.importActual()vi.hoisted()
- Hoist mock calls
- 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.
Activity
HerrDerb commentedon Mar 2, 2026
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.gcoadour commentedon Mar 2, 2026
Related to #31609
MillerSvt commentedon Mar 4, 2026
@alan-agius4 let's continue here.
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.mockand related calls at compile-time, and transform it for tests bundle. I can createng-automocks-vitestplugin and implement this mocks on my own.MillerSvt commentedon May 28, 2026
Can I try to make pull request for this to push it forward?