David Ren-Takahashi

4 stories by David Ren-Takahashi

Owning Session State Across Stripe and Kalshi Auth Flows in Integration Tests

Test stateful APIs by explicitly owning credentials and session state across API boundaries.

Understanding PayPal's state machine prevents payment failures during order processing.

Stripe's refund model breaks down in partial refunds, API changes, and payment method rules.

Understanding idempotency keys prevents duplicate charges and webhook processing errors.