Upgrading from SharePoint 2010 to SharePoint 2013 - Resolve Test-SPcontentDatabase Errors

Solution:

Try to install all custom solution in your new SharePoint 2013 environment before running the Test-SPcontentDatabase command.

Run Test-SPcontentDatabase command and generate a report.

Use SharePoint Feature Administration from Codeplex to clean up all MissingFeatures. You can do it by clicking here.

You  can also use PowerShell and link is available  here.