I think every developer working with SharePoint
2010 Migration might have seen issues related to MissingFeature and MissingWebPart
in Test Content DB report file. Depending on site customization, we may ignore
MissingWebPart category because it is not going to block us from migrating site
to SharePoint 2010. still it is always good to resolve every issues identify
into Test Content DB report.
Here is very good link which is describing how
to troubleshoot and resolve issue related to MissingFeature and MissingWebPart:
http://blogs.msdn.com/b/paulking/archive/2011/10/05/removing-missingfeature-database-amp-missingwebpart-webpart-class-errors-from-sharepoint-2010.aspx
Happy Migration!