Refactor of the serialization tests cont.

The continued refactoring basically consists of freeing the class with the test methods from the details by putting them in a helper class and renaming that makes the tests clearer. It also solves the problem in two of the Yaml files which depend on local types from the test assembly.

Commit 014d25e might be controversial. It moves the details of creating and tracking the sut's but could possibly make it harder to see what goes on..