VitestでIn-source testing

code: src/index.ts

// the implementation

export function add(...args: number[]) {

return args.reduce((a, b) => a + b, 0)

}

// in-source test suites

if (import.meta.vitest) {

const { it, expect } = import.meta.vitest

it('add', () => {

expect(add()).toBe(0)

expect(add(1)).toBe(1)

expect(add(1, 2, 3)).toBe(6)

})

}