mockingbird

Presentation

This lib provide a custom module loader to help write tests for modules.

It is compatible with the native nodejs test runners.

Getting started

Choose your favourite package manager.

pnpm add @vitruvius-labs/mockingbird

yarn add @vitruvius-labs/mockingbird

npm install @vitruvius-labs/mockingbird

Documentation

To use a mock in your test, use the mockingbird() function

mockingbird<TestedModule>(
	module_identifier: string,
	meta_url: string,
	mocks: Record<string, MockedDependency>
): TestedModule;

interface MockedDependency
{
	default: unknown;
	[imported: string]: unknown;
}

module_identifier is the module you want to test. Usually provided by the relative file path to it.

meta_url is simply the value of import.meta.url. It is used to resolve paths.

mocks is a mapping of the module dependencies to replace and with what to replace them.

If you have aliases in your imports, you must name the imported items by their original name.

The default import for a dependency can be filled under the default name.

Import syntax

Unsupported syntax for imports:

import defaultExport, { export1 } from "module-name";
import defaultExport, * as name from "module-name";

You can replace them with these syntax:

import { default as defaultExport, export1 } from "module-name";

// "defaultExport" can be accessed with "name.default"
import * as name from "module-name";

Example of use

Module file

import { randomUUID as seed } from "node:crypto";
import * as formatter from "./formatter.mjs";
import validateId from "./validate-id.mjs";

function generateId(): string
{
	const ID: string = formatter.formatId(seed());

	if (!validateId(ID))
	{
		throw new Error(`Invalid ID: ${ID}`);
	}

	return ID;
}

export { generateId };

Test file

import type * as TestedModule from '../src/my-module.mjs';

const MODULE: typeof TestedModule = await mockingbird<typeof TestedModule>(
	"../src/my-module.mjs",
	import.meta.url,
	{
		"node:crypto": {
			randomUUID: (): string =>
			{
				return "fixed-uuid";
			}
		},
		"./validateId.mjs": {
			default: (): boolean =>
			{
				return true;
			}
		},
	}
);

assert.doesNotThrow((): void => { MODULE.generateId(); });
assert.strictEqual(MODULE.generateId(), "fixed-uuid");