feat: Add missing unit tests and allow to generate code coverage

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

README.md

@@ -1,6 +1,5 @@
 # @nextcloud/event-bus
-[![Build Status](https://img.shields.io/github/actions/workflow/status/nextcloud/nextcloud-event-bus/node.yml?branch=master)](https://github.com/nextcloud/nextcloud-event-bus/actions/workflows/node.yml?query=branch%3Amaster)
-[![npm](https://img.shields.io/npm/v/@nextcloud/event-bus.svg)](https://www.npmjs.com/package/@nextcloud/event-bus)
+[![Build Status](https://img.shields.io/github/actions/workflow/status/nextcloud/nextcloud-event-bus/node.yml?branch=master)](https://github.com/nextcloud/nextcloud-event-bus/actions/workflows/node.yml?query=branch%3Amaster) [![Code coverage](https://img.shields.io/codecov/c/gh/nextcloud/nextcloud-event-bus/master)](https://app.codecov.io/gh/nextcloud/nextcloud-event-bus) [![npm](https://img.shields.io/npm/v/@nextcloud/event-bus.svg)](https://www.npmjs.com/package/@nextcloud/event-bus)
 [![Documentation](https://img.shields.io/badge/Documentation-online-brightgreen)](https://nextcloud.github.io/nextcloud-event-bus/)
 
 A simple event bus to communicate between Nextcloud components.

jest.config.ts

@@ -0,0 +1,13 @@
+import type { JestConfigWithTsJest } from 'ts-jest'
+import pkgJson from './package.json'
+
+const jestConfig: JestConfigWithTsJest = {
+	preset: 'ts-jest/presets/default',
+	testEnvironment: 'jsdom',
+
+	globals: {
+		__pkg_version: pkgJson.version
+	}
+}
+
+export default jestConfig