IoT test cases, for the fleet that reconnects all at once

Every defect in an IoT system is multiplied by the number of units in the field, and the units cannot be patched as easily as a server. That changes which cases matter. A shared credential across a batch means compromising one device compromises every device ever shipped, and there is no way to recall them. A reconnection strategy without randomised backoff means the whole fleet arrives in the same second when an outage ends, so the platform recovers and is immediately taken down by its own devices. Neither of these is visible when testing with one device on a desk.

Offline behaviour is the second theme. A device that buffers while disconnected is doing the right thing, but the reconnection is where it goes wrong: uploading the entire backlog at full speed floods the ingest, and doing that across many devices at once is indistinguishable from an attack. Paced upload solves it. Alongside that sit the data correctness cases, since buffered readings arrive out of order and must be stored by their reading timestamp rather than their arrival time, and unreliable links mean the same reading will sometimes be delivered twice.

Time is a genuine hazard on constrained hardware. A device with no real time clock has no idea what time it is after a power cycle, and readings stamped in 1970 will silently distort every aggregate they land in. The related case is distinguishing a missing reading from a zero: a sensor that has stopped reporting is not a sensor measuring nothing, and rendering them the same way turns an outage into an apparently valid measurement.

Commands need more care than telemetry because they act on the physical world. A command queued while a device is offline and delivered hours later can be actively unsafe, so expiry is a requirement rather than a refinement. The interface has to reflect the acknowledged state rather than the requested one, otherwise a switch that failed to actuate is displayed as on. And local network access needs its own authentication, because an unauthenticated local API means anyone on the same network controls the device regardless of how well the cloud path is secured.