music_library/backlog/completed/ml-6 - Align-mix.exs-test-coverage-threshold-with-sandbox-achievable-level.md

id, title, status, assignee, created_date, labels, dependencies, references, priority

id	title	status	assignee	created_date	labels	dependencies	references	priority
ML-6	Align mix.exs test coverage threshold with sandbox-achievable level	Done		2026-04-20 08:48			https://github.com/cloud8421/music_library/issues/177	low

Description

GitHub: created 2026-04-16 · updated 2026-04-17 · closed 2026-04-17

Summary

mix.exs sets a coverage threshold of 90 % but actual coverage is 75.77 %. Most of the 14.2-point gap is modules that legitimately cannot execute in the Ecto sandbox: cron-only workers (RepoVacuum, RepoOptimize, SendRecordsOnThisDayEmail, RefreshScrobbles) and Mix tasks. Per project conventions, tests for untestable sandbox operations are not written.

Evidence

Current coverage output: 75.77 % (720 tests, mix test --cover).

0 % modules that cannot be covered under the sandbox convention:

• MusicLibrary.Worker.RepoVacuum
• MusicLibrary.Worker.RepoOptimize
• MusicLibrary.Worker.SendRecordsOnThisDayEmail
• MusicLibrary.Worker.RefreshScrobbles
• MusicLibrary.Worker.BackfillScrobbledTracks
• Several Mix.Tasks.*

Why It Matters

A red coverage check on mix test --cover that is structurally unachievable trains contributors to ignore the signal. Either the threshold should reflect reality, or the untestable modules should be decorated for exclusion.

Fix (options)

1. Lower the threshold to a realistic value (e.g. 85 %) that fails when new gaps appear but passes today.
2. Decorate the unreachable modules with @moduledoc tags: [:skip_coverage] (or similar) and exclude them via test_coverage: [ignore_modules: [...]] in mix.exs.

Option 2 is preferable because it keeps the threshold aspirational and surfaces the exclusion list.

Acceptance Criteria

• mix test --cover passes under its configured threshold
• Untestable modules are explicitly enumerated somewhere (config, moduledoc, or both)

• #1 mix test --cover passes under its configured threshold
• #2 Untestable modules are explicitly enumerated somewhere (config, moduledoc, or both)