We have a live communication modern site, and i want to duplicate this site and all its content into a test site so i can test things before modifying the live. so is this possible inside SharePoint online? or are there any free tools to achieve this?
Probably your best option is using the PnP Provisioning Framework. This framework was initially started as a better approach to templating, intending to replace the classic web templates and site definitions, but has grown into much more.
Although there are numerous options that I won't cover here, a basic script using the Provisioning Framework in PnP-PowerShell would look something like this:
$sourceConn = Connect-PnPOnline -Url https://yoursite.sharepoint.com/sites/site1 -UseWebLogin -ReturnConnection $destConn = Connect-PnPOnline -Url https://yoursite.sharepoint.com/sites/site2 -UseWebLogin -ReturnConnection Get-PnPProvisioningTemplate -Out template.pnp -connection $sourceConn Apply-PnPProvisioningTemplate -Path template.pnp -connection $destConn