As smacdonald2008 mentioned please give details on how the Unit tests were set up and also please share the client sdk version being used at your end. It would have version something like 4.1.xx if you are using AEM Forms 6.3.
You need to add Adobe AEMDS Core Document Manager Support (adobe-aemds-core-docmanager) bundle in classpath or you can add it dependency. This bundle is present in AEM. It will resolve DocumentSourceHandler class