@type-challenges/utils

Testing utilities for TypeScript type challenges

The @type-challenges/utils package provides a comprehensive set of type-level utilities for testing and validating TypeScript types. These utilities enable you to write type assertions that are evaluated at compile time.

Installation

npm install -D @type-challenges/utils

Usage

Import the utilities you need in your TypeScript files:

import type { Equal, Expect, ExpectTrue, ExpectFalse } from '@type-challenges/utils'

type cases = [
  Expect<Equal<MyType, ExpectedType>>,
  ExpectTrue<SomeCondition>,
  ExpectFalse<AnotherCondition>,
]

Available Utilities

Assertion Utilities

• Expect - Generic type assertion wrapper
• ExpectTrue - Assert a type resolves to true
• ExpectFalse - Assert a type resolves to false
• ExpectExtends - Assert a value type extends an expected type
• ExpectValidArgs - Assert function arguments are valid

Comparison Utilities

• Equal - Deep equality check between two types
• NotEqual - Inverse of Equal
• Alike - Structural equality with merged intersections

Type Detection

• IsAny - Detect if a type is any
• NotAny - Inverse of IsAny
• IsTrue - Assert a type is true
• IsFalse - Assert a type is false

Advanced Utilities

• Debug - Expand type for better readability
• MergeInsertions - Recursively merge object intersections
• UnionToIntersection - Convert union types to intersection types

Type Testing Pattern

The standard pattern for type testing in Type Challenges is to create a type alias containing a tuple of test cases:

import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Result1, Expected1>>,
  Expect<Equal<Result2, Expected2>>,
  // ... more test cases
]

If any assertion fails, TypeScript will produce a compile-time error, indicating which test case failed.

Error Testing

You can test that certain type operations should produce errors using the @ts-expect-error directive:

// @ts-expect-error - This should fail
MyType<InvalidArgument>