Merge test coverage

[Xiaobin-0606]

How to merge test coverage of subpackages in a monorepo?

[AriPerkkio]

Use Vitest projects (workspaces) and coverage is automatically merged for whole project. Example at https://stackblitz.com/~/edit/vitest-workspace-coverage-fqtzap4y?file=vitest.config.ts.

import { defineConfig } from 'vitest/config'

export default defineConfig({
  test: {
    coverage: { enabled: true },
    projects: ['packages/*'],
  },
})