> Maybe you can be a bit more specific on what exactly you are trying to
> achieve and then people can come up with more concrete answers.

I wanted to understand what i must check and how to have 
a stable code.

are these rules right in general?

The imput comes directly from an external source:
  - Test with test units.
  - Check type and attinence to specifics of data.
  
The imput doesn't come from directly from an external source:   
  - Test with test units.
  - Don't care about type (duck typing).




-- 
>here are more things in heaven and earth,
horatio, than are dreamt of in your philosophy.