You need at least Magento 2.3 to use this version of the tool.

This tool bootstraps Magento2 with it's object manager factory, so every new dynamic class request will go through it and it will be created by Magento before phpspec tries to use it

Add the repository into your composer.json file using the following command:

composer config repositories.nagno git https://github.com/nagno/phpspec-bootstrap-magento2.git

Install the package:

composer require nagno/phpspec-bootstrap-magento2 --dev

Add these lines to phpspec.yml:

extensions:
    Nagno\Phpspec\BootstrapMagento2\Bootstrap: ~

This tool is compatible with PhpSpec 2, 4, 5 and 6.