To set up run below command

composer install

To test Matomo core

./vendor/bin/phpcs --report-full --standard=Matomo/ruleset.xml --report-checkstyle=./phpcs-report.xml /path/to/matomo

To test your plugin repository execute below command

./vendor/bin/phpcs --report-full --standard=Matomo/ruleset.xml --report-checkstyle=./phpcs-report.xml /path/to/matomo/plugins/GoogleAnalyticsImporter/