ts-test-utils

A collection of helper TypeScript types to test other TypeScript types. This collection so far includes:

• Expect - The main helper; Use this with the below types
• Equals - Check for equality between two types
• Assignable - Check if one type is assignable to another type
• Excludes - Check if a type doesn't contain another type
• Includes - Check if a type includes another type
• Extends - Check if one type is extending another type
• IsArray - Checks if a type is an array
• IsNotArray - Checks if a type is not an array
• Length - Check a given types length; Combine this with the 'Equals' type checker
• Position - Returns a type in the given position of an array; Combine this with the 'Equals' type checker
• IsNullable - Check if a type is nullable
• IsNonNullable - Check if a type is not nullable
• IsUndefined - Check if a type is undefined
• IsNonUndefined - Check if a type is not undefined
• IsNullish - Check if a type is either undefined or null
• IsNonNullish - Check if a type is neither undefined or null

Installation

To install ts-test-utils with Bun, run the following command:

bun i -D @crbroughton/ts-test-utils

Getting Started

You can use these types to test other types:

// This should return true
type Result = Expect<Equals<{ id: number }, { id: number }>>

For testing types that are expected to not equal each-other, you can add the //@ts-expect-error comment to tell the TypeScript compiler that a false return is expected, and that a match is not expected:

// @ts-expect-error - Object / Record failing the equality checker
type ResultRecord = Expect<Equals<{ id: number }, { id: string }>>

You can combine these types with existing types. As an example, here is the 'Equals' type being used to check a functions return type:

function myFunction() {
    return {
        id: 1,
        name: 'Craig',
    }
}
type Result = Expect<Equals<ReturnType<typeof myFunction>, { id: number, name: string }>>

Development Installation

To install dependencies:

bun install

To run:

bun run index.ts

This project was created using bun init in bun v1.1.3. Bun is a fast all-in-one JavaScript runtime.