Test code is too strict

[TripleDogDare]

In strict mode, serum should not complain about functions which return errors in _test.go files. These functions are unexportable in the sense that they can't be imported by other packages, even if they are exported in the sense that they can be implement required interfaces for the packages being tested.

Exceptions:

• A function that is explicitly annotated with errors should still be examined the same way as other unexported functions with annotations.