In the previous post on architecture, I argued that a good KMP suite is a consequence of architecture: keep the core framework-free, depend on ports, and most of your behavior becomes pure commonTest that runs without a device. That covered the fast tiers. This post is about the two slow ones that everybody actually fights with — screenshot tests and on-device benchmarks.
They're the flakiest tiers in any mobile suite. A snapshot that passes on your laptop and fails in CI; a startup benchmark that swings 40% run to run. The usual reaction is to distrust the tools and stop gating on them. But the flakiness almost never comes from Paparazzi or Macrobenchmark — it comes from non-determinism leaking into the thing under test. And the same component separation that powers the WeatherConditions core is exactly what seals those leaks.
Where the flakiness actually comes from
A screenshot diff and a benchmark number are both functions of their inputs. If any input wobbles, the output wobbles:
Source of wobble
