Makin’ Objects

"By de-coupling the tests from the existence of the subclasses, we have
given ourselves freedom to change inheritance without affecting any
model code."
Times We’re Livin’ In

"Are the teeny-tiny steps feeling restrictive? Take bigger steps. Are
you feeling a little unsure? Take smaller steps. TDD is a steering
process—a little this way, a little that way. There is not right step
size, now and forever."
The Root of all Evil

in refactor phase we finnaly got rid of Franc and Dollar classes.
Addition, Finally
Make It