Then you open antix.list in Terminal with:
sudo /etc/apt/sources.list.d/antix.list
In second out of three groups, you should find it.
You are looking for the line with “… stretch test” at the end:
# MX Community Main and Test Repos
deb http://nl.mxrepo.com/mx/repo/ stretch main non-free
#deb http://nl.mxrepo.com/mx/testrepo/ stretch test
… and you TEMPORARILY remove ‘#’ at the beginning of the line.
No sign == enabled; With sign == disabled
You don’t want the one starting with ‘src-deb’, but the one that has only ‘deb…’ at the beginning.
Part (path) before may vary, depending on your configuration (from which repo you are downloading from).
After you removed ‘#’ and saved the file, you open the Terminal and execute:
sudo apt-get update
sudo apt-get install ... whatever you're trying to install
After you’re done, you repeat the process and DISABLE (set ‘#’ at the beginning of the line) the testing repository again and execute:
sudo apt-get update
Now your antiX forgot about testing again.