suspicious_invoice_preview.rb

# setup
customer = Stripe::Customer.create(email: 'bob@bobsburgers2.soy')
customer.sources.create(source: { object: 'card', exp_month: 12, exp_year: 22, number: '4242424242424242', cvc: 123 })

coupon = Stripe::Coupon.create(id: 'THEDUDEABIDES_2', duration: 'forever', percent_off: 25)

plan_month_1 = Stripe::Plan.create(id: 'tmp_monthly_plan_1', name: 'MONTH 1', interval: 'month', amount: 9900, currency: 'usd')
plan_month_2 = Stripe::Plan.create(id: 'tmp_monthly_plan_2', name: 'MONTH 2', interval: 'month', amount: 9900, currency: 'usd')
plan_year = Stripe::Plan.create(id: 'tmp_annual_plan', name: 'YEAR  1', interval: 'year', amount: 999900, currency: 'usd')

# plan_month_1 = Stripe::Plan.retrieve('tmp_monthly_plan_1')
# plan_month_2 = Stripe::Plan.retrieve('tmp_monthly_plan_2')
# plan_year = Stripe::Plan.retrieve('tmp_annual_plan')

subscription = Stripe::Subscription.create(customer: customer.id, coupon: coupon.id, items: [{ plan: plan_month_1.id, quantity: 1 } ])
subscription_year = Stripe::Subscription.create(customer: customer.id, coupon: coupon.id, items: [{ plan: plan_year.id, quantity: 1 } ])

#
# TEST 0 (passes)
#
# confirm a discount exists on subscription
#
raise 'coupon applied but not on susbcription' if subscription.discount.nil?

#
# TEST 1 (passes)
#
# preview an invoice going from month -> month, without trying to clear out the coupon
#
plans_to_remove = subscription.items.data.map { |item| { id: item.id, deleted: true } }
plans_to_add = [{ plan: plan_month_2.id, quantity: 1 }]
plan_changes = plans_to_remove + plans_to_add
invoice_for_month_to_month_upgrade = Stripe::Invoice.upcoming(customer: customer.id, subscription: subscription.id, subscription_items: plan_changes, subscription_prorate: true)

raise 'I expect a coupon but it\'s not there' if invoice_for_month_to_month_upgrade.discount.nil?

#
# TEST 2 (passes)
#
# preview an invoice going from month -> month, and clear out the subscription's coupon
#
invoice_for_month_to_month_upgrade = Stripe::Invoice.upcoming(coupon: '', customer: customer.id, subscription: subscription.id, subscription_items: plan_changes, subscription_prorate: true)

raise 'I said no coupon! but there\'s a coupon' unless invoice_for_month_to_month_upgrade.discount.nil?

#
# TEST 3 (fails)
#
# now try previewing an invoice going from MONTH -> YEAR
plans_to_remove_2 = subscription.items.data.map { |item| { id: item.id, deleted: true } }
plans_to_add_2 = [{ plan: plan_year.id, quantity: 1 }]
plan_changes_2 = plans_to_remove_2 + plans_to_add_2
invoice_for_month_to_year_upgrade = Stripe::Invoice.upcoming(coupon: '', customer: customer.id, subscription: subscription.id, subscription_items: plan_changes_2, subscription_prorate: true)

# drumroll.....
# drumroll.....
raise '(month->year) I said no coupon! but there\'s a coupon' unless invoice_for_month_to_year_upgrade.discount.nil?

#
# Going from year to month also fails but I can't tell if it's actually applying the discount to the amount on the newly added monthly plan:
#
# TEST 4 (fails)
#
# now try previewing an invoice going from YEAR -> MONTH
plans_to_remove_3 = subscription_year.items.data.map { |item| { id: item.id, deleted: true } }
plans_to_add_3 = [{ plan: plan_month_1.id, quantity: 1 }]
plan_changes_3 = plans_to_remove_3 + plans_to_add_3
invoice_for_year_to_month_upgrade = Stripe::Invoice.upcoming(coupon: '', customer: customer.id, subscription: subscription_year.id, subscription_items: plan_changes_3, subscription_prorate: true)

raise '(year->month) I said no coupon! but there\'s a coupon' unless invoice_for_year_to_month_upgrade.discount.nil?