RPM of PHPUnit version 7.3 are available in remi repository for Fedora ≥ 25 and for Enterprise Linux (CentOS, RHEL…).
This new major version requires PHP ≥ 7.1 and is not backward compatible with previous versions, so the package is designed to be installed beside version 5 and 6.
dnf --enablerepo=remi install phpunit7
Installation, Enterprise Linux:
yum --enablerepo=remi install phpunit7
Notice: this tool is an essential component of PHP QA in Fedora. This version will quickly be available in Fedora 28.