=== calculate_commission() — pure logic ===
PASS: 5% of GHS 100 = GHS 5.00
PASS: 5% of USD 250 = USD 12.50 (commission takes the donation currency)
PASS: 10% of GHS 33.33 rounds to GHS 3.33
PASS: flat GHS 10 commission on a USD 5000 gift -- flat fee stays in the platform default currency, not the donation currency
PASS: 5% of a GHS 1 gift is still recorded correctly (GHS 0.05)

=== record_commission_for_donation() — DB-touching, idempotent ===
PASS: commission recorded for a donation on a referred event
PASS: commission amount is 5% of the donation (GHS 5.00)
PASS: commission attributed to the correct affiliate
PASS: new commission starts accrued
PASS: confirming the same donation twice does not double-record commission
PASS: organic (non-referred) event donation records no commission
PASS: a failed (not successful) donation records no commission even if called directly
PASS: new rate (10%) applies to a donation confirmed after the rate change
PASS: earlier commission keeps the OLD rate it was calculated with, unaffected by the later change

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RESULTS: 14 passed, 0 failed
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