Axis 05 · Absence: Can this bad sequence ever happen?

Something that must never happen, whatever else happens first. A cancelled order is never shipped. This is not about one value; it is about the order of events over time.

A service scheduled a shipment when an order was confirmed, and cancelling the order did not cancel the shipment. Confirm, then cancel, then the shipment still went out.

Temporal<FulfilmentEvent>.Never<FulfilmentEvent.Cancelled, FulfilmentEvent.Shipped>((_, _) => true)
		

Also Always for a rule about every event, and Transitions for the legal order of events.

It drives your real service with random calls (confirm, cancel, in any order) on a virtual clock, records the events the service emits with their times, and checks the rule against that log. Nothing waits in real time.

Absence failed.

Rule broken cancelled-orders-are-never-shipped Noticed at +30s What happened Cancelled, then Shipped Events recorded +0s Confirmed +14s Cancelled +30s Shipped Calls made wait 47s, Confirm -> wait 14s, Cancel

Law A sequence the domain forbids never happens, whatever the calls and their timing. Consequence A forbidden state is reachable in production by a sequence nobody wrote a test for.

Smallest case found, after 4 shrinks. To run this case again: .Seed("bJG2B9wvdYq4")

How to read this:

• Events recorded is what the service did, with times relative to the first event.
• Calls made is what the test did to cause it: wait 11 seconds, confirm, wait 6 seconds, cancel.
• What happened names the forbidden sequence: Cancelled, then Shipped.

A scenario test picks one order of calls. The forbidden sequence happens under the order, or the timing, the author did not pick.

In docs-builder, the live build behind docs-builder serve is tested this way: its events must always arrive as start, then findings, then an end, whatever the saves and timing.

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