Something to consider when following the rollover steps outlined in the post below.
If the target farm (Test / Dev) is a later patch level than the Content database and Project Web App database, they will need to be upgraded after mounting.
Upgrade the content database using the Upgrade-SPContentDatabase command and the Project Web App using the Upgrade-SPProjectDatabase. In 2010 the 4 PWA databases used to upgrade when provisioning the PWA site, in 2013 this process fails due to the Project Web App database being in compatibility range. The error found in the upgrade log can be seen below:
OWSTIMER (0x27C4) 0x467C SharePoint Foundation Upgrade SPUpgradeSession aloop DEBUG Entering upgrade for [ProjectSite Name=8d511428-9d61-4731-96bd-28be45bfba6b] 72be219c-e53a-b0d0-1951-87ac137d4659
OWSTIMER (0x27C4) 0x467C SharePoint Foundation Upgrade SPUpgradeSession ajxnf ERROR Cannot upgrade [ProjectSite Name=8d511428-9d61-4731-96bd-28be45bfba6b]. 72be219c-e53a-b0d0-1951-87ac137d4659
OWSTIMER (0x27C4) 0x467C SharePoint Foundation Upgrade SPUpgradeSession ajxng DEBUG Skip upgrading [ProjectSite Name=8d511428-9d61-4731-96bd-28be45bfba6b]. 72be219c-e53a-b0d0-1951-87ac137d4659
OWSTIMER (0x27C4) 0x467C SharePoint Foundation Upgrade SPUpgradeSession alooy DEBUG Exiting upgrade for [ProjectSite Name=8d511428-9d61-4731-96bd-28be45bfba6b]. Elapsed Time=[00:00:00] 72be219c-e53a-b0d0-1951-87ac137d4659