Maven surefire forkMode pertest deprecated. What is the new settings?

That isn't mentioned in the documentation, but <forkMode>pertest</forkMode> is the same as always forking. This is the check in the code:

if ( "pertest".equalsIgnoreCase( forkMode ) )
{
    return FORK_ALWAYS;
}

This synonym was made during resolution of the JIRA issue SUREFIRE-96, where, quoting Brett Porter:

pertest and perTest still work, but I've changed it to "always" which seems consistent with "once", and also changed "none" to "never".

As such, you should migrate your current configuration of <forkMode>pertest</forkMode> to forkCount=1 and reuseForks=false, like mentioned in Migrating the Deprecated forkMode Parameter to forkCount and reuseForks.

You need to replace

<forkMode>pertest</forkMode> 

with

<forkCount>1</forkCount>
<reuseForks>false</reuseForks>