This extension ships with PHPUnit tests. The generic PHPUnit configuration in Magento 2 will pick up on these tests. To only test Yireo extensions, simply run PHPUnit from within this folder. Note that this assumes that the extension is installed via composer. For instance:
phpunit
Also note that Mockery (mockery/mockery) is used for the integration tests. If you want to test this module, you need to install its dev-dependencies:
composer require yireo/magento2-googletagmanager2 --dev
The JavaScript code ships with MochaJS unit tests. To install the stuff, simply run (within this extension directory) the following:
npm install
npm run mocha
Or just use yarn:
yarn
npm run mocha