For example:
order.status = "paid" order.invoiceId = null
No crash. No exception. Just wrong state.
How do experienced teams usually detect or guard against this kind of issue in real production systems?
For example:
order.status = "paid" order.invoiceId = null
No crash. No exception. Just wrong state.
How do experienced teams usually detect or guard against this kind of issue in real production systems?
For example, async flows where status updates and data creation are handled in different places.
Curious how teams make these kinds of assumptions explicit in practice.
The gap I’ve seen is that tests usually validate expected scenarios, while some invariants only break after specific sequences of events or over time — especially with async flows and state that evolves across renders.
In practice, we found tests and runtime checks to be complementary: tests verify intent, invariants catch unexpected drift when reality doesn’t match assumptions.
That’s where things get tricky to reason about upfront.
For example, in your example is there any situation where there is an invoice that has not been paid?
In the vast majority of shopping cart systems, that would be a hard NO. There would be an Order ID, for carts that have not yet been paid for, sure, but an Invoice ID only makes sense if the order has been fully paid for, and not at any stage previous to that.
As such, why have an Order Status at all? Have the mere presence of the Invoice ID be the flag that states the order has been paid for. As in: null = not paid, not null = paid.
The idea wasn’t to replace good modeling or tests, but to fail early when real-world state temporarily drifts away from its intended shape (especially in async or legacy flows).
I put a small prototype here if anyone’s curious: https://github.com/vortexshadow678-hash/invariant-guard
OsrsNeedsf2P•2w ago
vortexshadow•2w ago
Failing early is the key part — especially before invalid state has a chance to propagate through the system.
What I’ve found tricky in React apps is identifying where those invariants should live when the logic spans multiple async updates.
Do you usually enforce them close to state updates, or at higher-level boundaries?