> I am confused. 72 chars is a limit for the whole commit
> message? 

72 for commit message body, 50 for commit subject.

> I am confused again. What is this 80-chars constraint about?

This is *acceptable* limit of symbols per line in source code.
Notice, that for comments in code it is 66 chars.
Your fix violates this rule: line is about 84 chars.

Also, we are going to support static types soon,
so lets add types for all tests in your suite.