Unit tests

[myurkin]

This issue aims to to start some partial implementation of the unit tests. In general, ADDA is not well-suited for unit tests due to heavy use of global variables and complex code workflow. The problem is related to #200 . But a less ambitious goal is to implement unit testing for some (new) functions (at least, to understand the capabilities and limitations of existing tools for that). Even for that, #114 will probably simplify the implementation.

[myurkin]

/cc @palatni @dsmunev

[myurkin]

@palatni mentioned a simple framework for that - https://github.com/Snaipe/Criterion