Exercise the One Unproven Cell Before Launch

Before shipping, map every path in your system as a matrix and honestly mark which cells have actually been exercised end-to-end versus merely assumed to work. Most paths get incidental coverage during normal development; the dangerous ones are the cells that only activate under specific conditions — a time-gated mode, a rare payment path, an edge branch that never fires in daytime testing.

Reserve a final pre-launch pass for the single cell that has never run against real conditions. Simulated or mocked runs don’t count here: the whole point is to prove the integration seams where money, third-party services, and your own persistence layer all meet. If the real path only surfaces under a certain condition, run your test under exactly that condition — otherwise you’re validating a different path than the one that will carry live traffic.

When a live test moves real value, plan the reversal as part of the test itself: complete the transaction, capture the identifiers, then immediately undo it and verify the system returns to a net-zero, clean state with no downstream side effects triggered. Confirm every layer independently — the payment settled and reversed, the dependent service created and cleaned up its record, and your own store persisted the linkage correctly.

A clean end-to-end pass with no error alarms is the real go signal. Assumptions about untested cells are the failures you discover in production.