add test for merchant_repo revenue(date)
refactor merchant_repo#most_revenue(amount) method
add pry
updated most_revenue and most_items calcs, working locally, spec harness failing
new implementation of merchant_repo#most_items
update implementation of merchant_repository#most_items
new implementation of merch_repo most_revenue
most_revenue is passing spec harness, most_items failing spec harness
update dates on invoice_item to be Dates, WIP
get tests passing for merchant#revenue(date)
get tests passing for merchant_repo#revenue(date)