I'm trying to tell
sudo pear channel-discover pear.phpunit.de
Discovering channel pear.phpunit.de over http:// failed with message: channel-add: Cannot open "http://pear.phpunit.de/channel.xml" (File http://pear.phpunit.de:80/channel.xml not valid (received: HTTP/1.1 410 Gone
Trying to discover channel pear.phpunit.de over https:// instead
Discovery of channel "pear.phpunit.de" failed (channel-add: Cannot open "https://pear.phpunit.de/channel.xml" (File https://pear.phpunit.de:443/channel.xml not valid (received: HTTP/1.1 410 Gone
sudo pear channel-update pear.php.net
sudo pear upgrade-all
sudo pear config-set auto_discover 1
sudo pear install pear.phpunit.de/PHPUnit
Attempting to discover channel "pear.phpunit.de"...
Attempting fallback to https instead of http on channel "pear.phpunit.de"...
unknown channel "pear.phpunit.de" in "pear.phpunit.de/PHPUnit"
invalid package name/package file "pear.phpunit.de/PHPUnit"
You can't install phpunit using pear anymore: https://github.com/sebastianbergmann/phpunit/wiki/End-of-Life-for-PEAR-Installation-Method
But you can still install it using the phar file: https://phpunit.de/getting-started.html
Or using composer: https://phpunit.de/manual/current/en/installation.html#installation.composer