Collect distributed coverage before stopping peers - #6
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Problem
Coverage instrumentation changes the coordinator's compiled helper functions, but distributed peers load ordinary BEAM files. This causes remote
badfunfailures undermix test --cover. Peer execution is also absent from the report unless its counters are collected before the VM stops.Fix
Enable distributed OTP coverage and attach each peer before starting Group. OTP loads the same instrumented modules on the peers, preserving anonymous-function compatibility and collecting their execution.
Route all peer shutdowns, including deliberate node-failure scenarios, through a coverage-aware helper that transfers counters before stopping the VM. Exclude support modules from the reported score and add a regression that checks retention of a peer-only call after shutdown.
Supporting information
The combined coverage report is approximately 84.7%, below Mix's unchanged default 90% threshold. Consequently,
mix test --coverstill exits nonzero for the coverage threshold, rather than remote execution failures. This change does not lower the threshold or conceal the coverage gap.Abrupt VM crashes can still lose counters not yet collected; the deliberate shutdown helper collects them first.