How to start unit tests for powermail?

On command line

First of all go to powermail folder in console
Then do a composer update
After that you can call /usr/bin/php .Build/vendor/phpunit/phpunit/phpunit --configuration phpunit.xml.dist

In PhpStorm

First of all got to powermail folder in console
Then do a composer update
After this, you should open the PhpStorm Settings and go to Languages & Frameworks > PHP > Test frameworks
Choose use composer autoloader
Add folder on path to script to EXT:powermail/.Build/vendor/autoload.php
Finish: Right-Click on file phpunit.xml.dist with Run 'phpunit.xml.dist'

With code coverage

You need to have xdebug installed and configured on your test environment
On command line you can run it like /usr/bin/php -dxdebug.coverage_enable=1 .Build/vendor/phpunit/phpunit/phpunit --configuration phpunit.xml.dist --coverage-text
In PhpStorm you could simply right-click on file phpunit.xml.dist with Run 'phpunit.xml.dist with Coverage'

Screenshot

Example of code coverage in PhpStorm: