colinhacks/typejest

bun add -d typejest
npm add -D typejest
yarn add -D typejest
pnpm add -D typejest

import {texpect} from 'typejest';

// you can pass in a value
texpect('tuna'); // TExpect<string>

// or pass in a type directly
texpect<string>(); // TExpect<string>

import {texpect} from 'typejest';

texpect('tuna').is<string>(); // assert value is of type
texpect<string>().is<string>(); // assert two types are equal

texpect('tuna').is<string>();
texpect<string>().is<string>();

const value = 'asdf';

texpect(value).extends<string | number>(); // true
texpect<string>().extends<string | number>(); // true

texpect('asdf').string();
texpect(123).number();
texpect(true).boolean();
texpect(false).boolean();
texpect(Symbol()).symbol();
texpect(BigInt(123)).bigint();
texpect({}).object();
texpect(() => {}).function();
texpect<any[]>().array();
texpect(null).null();
texpect(undefined).undefined();
texpect<never>().never();
texpect<unknown>().unknown();
texpect<void>().void();

type Dog = {name: string; age?: number};

texpect<Dog>().partial; // TExpect<Partial<Dog>>
texpect<Dog>().required; // TExpect<Required<Dog>>
texpect<Dog>().keyof; // TExpect<keyof Dog>

texpect<Dog>().pick<'name'>; // TExpect<Pick<Dog, "name">>
texpect<Dog>().pick('name'); // TExpect<Pick<Dog, "name">>

texpect<Dog>().omit<'name'>; // TExpect<Omit<Dog, "name">>
texpect<Dog>().omit('name'); // TExpect<Omit<Dog, "name">>

texpect<Dog>.keyof.is<"name" | "age">();
texpect<Dog>.pick("name").is<{ name: string }>();
texpect<Dog>.partial.is<{ name?: string; age?: number; }>();

const value = ['string', 234] as const;

texpect<typeof value>().first<'string'>();
texpect<typeof value>().last<234>();

function length(arg: string) {
  return arg.length;
}

texpect<typeof length>().returns<number>();
texpect<typeof length>().accepts<[string]>();