The Umbraco HQ team has done a great job with the tests, and the testing architecture. I have done a few small changes, e.g. moving the test database over to MySql by way of an MySqlTestHelper.
At present about 269 /500 tests are passing. Some of the failing tests pass when run individually. This has been a slow laborious process, and Monodevelop has been frequently freezing after failing tests.
I will need to update my own test (4.7.2) code at some point. I am using it here but it is not a good architectural match, and will need to be refactored.
For compatibility it might be good in the future to move the test database to SqlLite - or another db that can be used in Windows and non-Windows environments.