billing: Create cents_to_dollar_string helper function.

corporate/lib/stripe.py

@@ -190,6 +190,10 @@ def get_idempotency_key(ledger_entry: LicenseLedger) -> Optional[str]:
     return f"ledger_entry:{ledger_entry.id}"  # nocoverage
 
 
+def cents_to_dollar_string(cents: int) -> str:
+    return f"{cents / 100.:,.2f}"
+
+
 class BillingError(Exception):
     # error messages
     CONTACT_SUPPORT = gettext_lazy("Something went wrong. Please contact {email}.")

corporate/views.py

@@ -17,6 +17,7 @@ from corporate.lib.stripe import (
     MIN_INVOICED_LICENSES,
     STRIPE_PUBLISHABLE_KEY,
     BillingError,
+    cents_to_dollar_string,
     do_change_plan_status,
     do_replace_payment_source,
     downgrade_at_the_end_of_billing_cycle,
@@ -332,7 +333,7 @@ def billing_home(request: HttpRequest) -> HttpResponse:
                 licenses_at_next_renewal=licenses_at_next_renewal,
                 seat_count=seat_count,
                 renewal_date=renewal_date,
-                renewal_amount=f"{renewal_cents / 100.:,.2f}",
+                renewal_amount=cents_to_dollar_string(renewal_cents),
                 payment_method=payment_method,
                 charge_automatically=charge_automatically,
                 publishable_key=STRIPE_PUBLISHABLE_KEY,