V8 Coverage showing unexpected results

Bắt đầu bằng cách tái hiện trên Angular 21 bằng ng test --coverage, sau đó kiểm tra angular.json và vitest.config.ts cùng với các thay đổi trong app.ts và app.spec.ts. So sánh báo cáo branch của V8 cho component rỗng với các include và exclude coverage đã cấu hình. Được coi là hoàn tất khi xác định được kết quả là hành vi V8 như mong đợi hay là lỗi trong unit-test builder của Angular CLI, kèm theo một trường hợp có thể tái hiện và tài liệu mô tả hành vi coverage mong đợi.

Which @angular/* package(s) are the source of the bug?

Don't known / other

Is this a regression?

No

Description

I'm in the process of migrating from jasmine/karma with istanbul coverage to vitest with v8 coverage. I'm currently migrating around 2500 unit tests. With Istanbul I had over 95% coverage across statements, branches, functions and lines. With vitest I'm seeing lower coverage, mainly on the branches with 90%.

I've noticed that even empty classes (template only) show 90% branch coverage (9/10).

A minimal reproduction:

• Create a new Angular 21 application: ng new ng21
• Install v8 coverage npm i --save-dev @vitest/coverage-v8
• Remove the protected title variable from app.ts -- protected readonly title = signal('ng21');
• Remove the should render title test from app.spec.ts
• Run ng test --coverage

This is the coverage I see:

Similar from my project:

with the spec file as:

import { TestBed } from '@angular/core/testing';
import { HeaderComponent } from './header.component';
import { HeaderComponent as ClsHeaderComponent, TenantDropdownComponent } from '@cls/ui-util';
import { MockComponent } from '@cls/ui-util/testing';
import { SearchComponent } from '../../schedule/components/search/search.component';

describe('HeaderComponent', () => {
    beforeEach(async () => {
        await TestBed.configureTestingModule({
            imports: [HeaderComponent],
            providers: []
        })
            .overrideComponent(HeaderComponent, {
                remove: { imports: [SearchComponent, ClsHeaderComponent, TenantDropdownComponent] },
                add: {
                    imports: [
                        MockComponent({ selector: 'app-search' }) as any,
                        MockComponent({ selector: 'cls-header' }) as any,
                        MockComponent({ selector: 'cls-tenant-dropdown' }) as any
                    ]
                }
            })
            .compileComponents();
    });

    function setup() {
        const fixture = TestBed.createComponent(HeaderComponent);

        return {
            fixture,
            app: fixture.componentInstance,
            compiled: fixture.debugElement.nativeElement
        };
    }

    it('should create the app', () => {
        const { app } = setup();
        expect(app).toBeTruthy();
    });
});

angular.json

"test": {
  "builder": "@angular/build:unit-test",
  "options": {
    "browsers": ["chromium"],
    "buildTarget": "admin-ui:build",
    "headless": true,
    "tsConfig": "./tsconfig.spec.json",
    "runnerConfig": "./vitest.config.ts",
    "coverage": true,
    "coverageInclude": ["src/app/**/*.ts"],
    "coverageExclude": ["index.ts", "main.ts", "polyfills.ts", "**/*.routes.ts", "**/*.model.ts", "**/*.interface.ts"],
    "coverageReporters": ["text", "html", "lcov"],
    "coverageThresholds": {
      "statements": 90,
      "branches": 90,
      "functions": 90,
      "lines": 90
    }
  }
}

vitest.config.ts

import { defineConfig } from 'vitest/config';

export default defineConfig({
    test: {
        environment: 'jsdom',
        globals: true,
        setupFiles: ['src/test-setup.ts'],
        restoreMocks: true,
        coverage: {
            provider: 'v8'
        },
        browser: {
            screenshotFailures: false
        }
    }
});

Have I misconfigured something? Do I have an incorrect assumption of v8 coverage or is there an issue here?

Please provide a link to a minimal reproduction of the bug

No response

Please provide the exception or error you saw

Please provide the environment you discovered this bug in (run ng version)

Angular CLI       : 21.2.3
Angular           : 21.2.5
Node.js           : 22.13.1
Package Manager   : npm 10.9.2
Operating System  : darwin arm64

┌───────────────────────────────────┬───────────────────┬───────────────────┐
│ Package                           │ Installed Version │ Requested Version │
├───────────────────────────────────┼───────────────────┼───────────────────┤
│ @angular/animations               │ 21.2.5            │ ~21.2.0           │
│ @angular/build                    │ 21.2.3            │ ^21.2.0           │
│ @angular/cdk                      │ 21.2.3            │ ~21.2.0           │
│ @angular/cli                      │ 21.2.3            │ ~21.2.0           │
│ @angular/common                   │ 21.2.5            │ ~21.2.0           │
│ @angular/compiler                 │ 21.2.5            │ ~21.2.0           │
│ @angular/compiler-cli             │ 21.2.5            │ ~21.2.0           │
│ @angular/core                     │ 21.2.5            │ ~21.2.0           │
│ @angular/forms                    │ 21.2.5            │ ~21.2.0           │
│ @angular/language-service         │ 21.2.5            │ ~21.2.0           │
│ @angular/platform-browser         │ 21.2.5            │ ~21.2.0           │
│ @angular/platform-browser-dynamic │ 21.2.5            │ ~21.2.0           │
│ @angular/router                   │ 21.2.5            │ ~21.2.0           │
│ rxjs                              │ 7.8.2             │ ~7.8.2            │
│ typescript                        │ 5.9.3             │ ~5.9.3            │
│ vitest                            │ 4.1.0             │ ^4.0.18           │
│ zone.js                           │ 0.15.1            │ ~0.15.0           │
└───────────────────────────────────┴───────────────────┴──────────────────

Anything else?

No response