Unit Testing on SharePoint only really begins to work properly when you mock the SharePoint object model using one of a few methods.
Andrew Woodward over at 21apps.com has documented his findings of this, particularly with using TypeMock Isolator for SharePoint.
I also seen a recent presentation of his which demonstrated UI Testing Features available in Visual Studio 2010 Ultimate, which was quite interesting.
(Slide Deck: http://www.21apps.com/sharepoint/slides-ui-testing-bpc10/)
For Load Testing, I have seen a good presentation from Steve Smith of Combined Knowledge about using Visual Studio for Load Testing a SharePoint farm. If you contact him through Twitter I'm sure he may be able to point you to resources regarding this: