The Essential Type Testing Tool.

Helpers

If you are used to test JavaScript, a simple type test file should look familiar:

import { expect, test } from "tstyche";
 
function firstItem<T>(target: Array<T>): T | undefined {
  return target[0];
}
 
test("firstItem", () => {
  expect(firstItem(["a", "b", "c"])).type.toBe<string | undefined>();
 
  expect(firstItem()).type.toRaiseError("Expected 1 argument");
});

To organize, debug and plan tests TSTyche has:

• test(), it() and describe() helpers,
• with .only, .skip and .todo run mode flags.

Assertions

The assertions can be used to write type tests (like in the above example) or mixed in your functional tests:

import assert from "node:assert";
import test from "node:test";
import * as tstyche from "tstyche";
 
function secondItem<T>(target: Array<T>): T | undefined {
  return target[1];
}
 
test("handles numbers", () => {
  assert.strictEqual(secondItem([1, 2, 3]), 2);
 
  tstyche.expect(secondItem([1, 2, 3])).type.toBe<number | undefined>();
});

Here is the list of all matchers:

• .toBe(), .toBeAssignableTo(), .toBeAssignableWith() compare types or types of expression,
• .toAcceptProps() checks JSX component props,
• .toHaveProperty() looks up keys on an object type,
• .toRaiseError() captures the type error message or code,
• .toBeString(), .toBeNumber(), .toBeVoid() and 9 more shorthand checks for primitive types.

Runner

The tstyche command is the heart of TSTyche. For example, it can select test files by path, filter tests by name and pass them through TypeScript 4.8 and latest:

tstyche JsonObject --only external --target 4.8,latest

This simple! (And it has watch mode too.)