jest/ts/ tests找不到名称'x‘

// example.ts
let x = 10;

// example.ts
export let x = 10;

// test.ts
import { x } from './example';

{
  "compilerOptions": {
    "target": "es6",
    "module": "commonjs",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  },
  "include": ["src/**/*.ts", "tests/**/*.ts"],
  "exclude": ["node_modules"]
}

// example.ts
namespace MyNamespace {
  export let x = 10;
}

// test.ts
/// <reference path="./example.ts" />
console.log(MyNamespace.x);

export let x = 10;

import { x } from './example';

test('x should be 10', () => {
  expect(x).toBe(10);
});

project-root/
├── src/
│   └── example.ts
├── tests/
│   └── example.test.ts
└── tsconfig.json

npx jest