Apologies if this has been asked previously I wish to upgrade my SharePoint Foundations 2013 Production system to the latest cumulative update and was wondering how to make a test clone of my production data so I can test the upgrade there first.

Many Thanks in advance

You cannot clone a SharePoint farm. The supported method is to create a new test farm and perform a backup and restore from your production farm to your test farm: 

In the test environment setup SQL Server and SharePoint, and patch it to the same level as your production farm. Create a new farm but don't configure any web apps or services.

Install any customizations you're using in production

Perform a full farm backup of production, and restore it to your new test farm. Note you'll need to restore to new locations so you can specify the servers in the test farm.

Validate the sites work as expected.

Once you've done all this you can install the updates. If this is a VM environment you can take a snapshot of all servers in the farm (turn them off first) or make a full backup so you have something to revert to if the updates go sideways.

Many thanks for the reply, if I may ask another daft question.

So I will need a full farm backup as opposed to backing up and restoring just the content databases?