use vitest typechecks

package.json

@@ -23,7 +23,6 @@
   },
   "devDependencies": {
     "@eslint/js": "9.7.0",
-    "@type-challenges/utils": "0.1.1",
     "@types/node": "20.14.11",
     "eslint": "9.7.0",
     "typescript": "5.5.3",

types/Branded.Age-Year.test.ts

@@ -0,0 +1,39 @@
+import { expect, expectTypeOf, test } from 'vitest'
+import { raise } from '../raise/index.js'
+import { Branded } from './Branded.ts'
+
+/** branded numbers */
+type Age = Branded<number, 'Age'>
+type Year = Branded<number, 'Year'>
+
+const validAge = (age: number): Age | undefined =>
+  age >= 0 && age <= 125 ? age as Age : undefined
+
+const birthYear = (age: Age, now: Date): Year =>
+  now.getFullYear() - age as Year // this is incorrect, but sufficient for demo purpose
+
+test('Age is compile-time save', () => {
+  const someAge = validAge(5) ?? raise('invalid age')
+
+  expectTypeOf(someAge).toEqualTypeOf<Age>()
+  expectTypeOf(someAge).not.toEqualTypeOf<number>()
+})
+
+test('birthYear is compile-time safe', () => {
+  const fiveYears = validAge(5) ?? raise('invalid age')
+
+  expectTypeOf(birthYear).parameters.toMatchTypeOf<[Age, Date]>()
+
+  const twothousandnineteen = birthYear(fiveYears, new Date(2024, 4, 11))
+  expect(twothousandnineteen).toBe(2019)
+
+  expectTypeOf(twothousandnineteen).toEqualTypeOf<Year>()
+  expectTypeOf(twothousandnineteen).not.toEqualTypeOf<number>()
+})
+
+test('birthYear\'s argument is still just a number in JS', () => {
+  expect(
+    // @ts-expect-error argument must be Age
+    birthYear(5, new Date(2024, 4, 11))
+  ).toBe(2019)
+})

types/Branded.Email.test.ts

@@ -0,0 +1,17 @@
+import { expectTypeOf, test } from 'vitest'
+import { raise } from '../raise/index.js'
+import { Branded } from './Branded.js'
+
+/** branded string */
+type Email = Branded<string, 'Email'>
+
+const emailRegex = /^[a-zA-Z0-9.!#$%&’*+/=?^_`{|}~-]+@[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$/ // a simplified regex
+const validEmail = (email: string): Email | undefined =>
+  emailRegex.test(email) ? email as Email : undefined
+
+test('Email is compile-time save', () => {
+  const someEmail = validEmail('[email protected]') ?? raise('invalid email')
+
+  expectTypeOf(someEmail).toEqualTypeOf<Email>()
+  expectTypeOf(someEmail).not.toEqualTypeOf<string>()
+})