Test Files

Loading "Move Tests Into Modules (🏁 solution)"

I start by creating a new greet.test.ts file and moving only the test(...) blocks there.

test('returns a greeting message for the given name', () => {
	expect(greet('John')).toBe('Hello, John!')
})

test('returns a congratulation message for the given name', () => {
	expect(congratulate('Sarah')).toBe('Congrats, Sarah!')
})

Which suffix to use: .spec.ts or .test.ts, or both?

If I try to run test test file now, it will exit on undefined greet() and congratulation() functions because they are neither defined nor imported from anywhere.

So I go and export those functions from the greet.ts module:

export function greet(name: string) {
	return `Hello, ${name}!`
}

export function congratulate(name: string) {
	return `Congrats, ${name}!`
}

And import them in the test file:

import { greet, congratulate } from './greet.js'

Next, I want to make the test() and expect() functions available globally. Every test will be using those, so there's no need to explicitly import them every time.

Next, I create a setup.ts file where I start by describing the test() and expect() functions in TypeScript. I add them to the global namespace to let TypeScript know those functions will be available globally, and that we don't have to import them.

interface Assertions {
	toBe(expected: unknown): void
}

declare global {
	var expect: (actual: unknown) => Assertions
	var test: (title: string, callback: () => void) => void
}

Then, I move the existing test() and expect() functions directly to the globalThis object to expose them globally on runtime and also benefit from the type inference since they are now fully annotated!

globalThis.expect = function (actual) {
	return {
		toBe(expected: unknown) {
			if (actual !== expected) {
				throw new Error(`Expected ${actual} to equal to ${expected}`)
			}
		},
	}
}

globalThis.test = function (title, callback) {
	try {
		callback()
		console.log(`✓ ${title}`)
	} catch (error) {
		console.error(`✗ ${title}`)
		console.error(error, '\n')
	}
}

All that remains is to verify that the tests are running correctly.

npx tsx --import ./setup.ts greet.test.ts

I am using the --import option in Node.js to load the setup.ts module before running greet.test.ts. This makes the test() and expect() functions globally available in the test's runtime.

02. Test Structure/03. Test Files (🏁 solution)

Test Files