onto counting coins
first failing test
silly test passes
haven't defined any coins
define coins
possible change
test fails, why?
fix silly mistake
rename
failing test for recursive case
still failing test, but sketched
test for the simplest base case
solve base case
my test wasn't very good
fix test expectations (still fails)
ah-ha, smaller, failing test case
now I understand, I'm not using a set
refactor
refactor
failing test