Set Ts Jest Isolated Modules

Set isolatedModules for ts-jest below TypeScript 6

The jest 30 path of @nx/jest bumps ts-jest to 29.4.x. On the CommonJS jest path, ts-jest 29.2+ uses moduleResolution: node10 when bundler is invalid alongside the forced module: commonjs, which is the case below TypeScript 6. node10 does not read package exports maps, so a workspace library that exposes types only through exports fails to resolve during the ts-jest type check:

error TS2307: Cannot find module '@my-org/some-lib' or its corresponding type declarations.

The migration sets isolatedModules: true in each affected tsconfig.spec.json, so ts-jest transpiles each file independently and skips the cross-file type resolution that was failing. This matches the isolatedModules: true that fresh ts-solution workspaces already set in tsconfig.base.json. Type checking stays on each project's dedicated typecheck target.

The migration runs only below TypeScript 6, in ts-solution workspaces that do not already enable isolatedModules. TypeScript 6 and above resolves exports under bundler with commonjs, so those workspaces are left unchanged.

Sample code changes

Before

{
  "extends": "../../tsconfig.base.json",
  "compilerOptions": {
    "types": ["jest", "node"]
  }
}

After

{
  "extends": "../../tsconfig.base.json",
  "compilerOptions": {
    "isolatedModules": true,
    "types": ["jest", "node"]
  }
}

Verifying the workspace

After the migration runs, verify the workspace still typechecks and fix anything isolatedModules surfaced:

nx run-many -t typecheck

isolatedModules can fail typecheck (TS1205 - re-exporting a type needs export type; TS2748 - const enum access) or break a project's tests at runtime even when typecheck passes. The cause is a package that re-exports a value through both module.exports and an ESM export (for example napi bindings exposing a const enum); per-file transpilation cannot preserve it, and consumers of that const enum break too. To fix a broken project, remove isolatedModules from its tsconfig.spec.json; if that brings back the TS2307: Cannot find module error this migration was added to prevent, that project needs isolatedModules, so fix the source instead.