I see you are aiming to be able to define a test is run third or second and other tests will be run around it to ensure it is in that position in the sequence. I am not sure how to implement that or when you would use the feature as it makes the tests very dependant upon one another.

The ordering I implemented was to make all things 0 run first then all things 1 then all 2, .... then lowest -negative up to -1. Any tests not marked with a sequence number get executed after all +ve numbers and before any -ve numbers.

So if you want a test to be run second (2) you must also specify the tests to run as first (1).

I expect it would be quite hard to implement a system that works out a pseudo sequence to create the 'second' executed test, and I am not sure when you would use it and not also need to specify the first test.

What may be better is to think how we can implement the before/after features (in your documentation driven design). it will need an exception raise when the order is not implementable (i.e. circular dependancies).