Coverage is measured differently locally and on CI, hiding 68 untested app files

The backend coverage figure means different things locally and on CI, and the local one is the misleading one. Reproduced exactly, not inferred.

$ bundle exec rspec              3772 / 3948 LOC (95.54%)
$ CI=true bundle exec rspec      4193 / 4856 LOC (86.35%)   # identical to CI's report

Cause

Two settings that are each fine alone:

• config/environments/test.rb — config.eager_load = ENV["CI"].present?. This is the stock Rails default, verbatim from the railties app template; nobody misconfigured it.
• spec/spec_helper.rb — a bare SimpleCov.start, with no profile and therefore no track_files.

Without track_files, SimpleCov measures only files that were actually loaded. GitHub Actions always sets CI=true, so Rails eager-loads all of app/; locally it does not, so only the files the specs happen to touch are loaded, and only those are measured.

What that hides

The delta accounts for itself exactly — 4856 − 3948 and 4193 − 3772:

70 files, 908 relevant lines, 421 covered. 68 of the 70 are app/ files, so 38% of the application is never loaded by the suite at all.

Those files are not reported as 0% locally. They are absent from the report. The local denominator is defined by what the tests already reach, which makes 95.54% close to circular.

The CI number is not trustworthy either, for a different reason: spec/ files are 1952 of its 4856 lines — 40% — at 98.51% covered, because the test_frameworks filter only ships with SimpleCov's rails profile, which is not loaded. The tests are grading themselves.

Honest figure for application code: 77.09%.

The 46% those 70 files appear to have on CI is pure load-time execution. Line by line on app/jobs/same_trackables_job.rb (18.2% on CI, invisible locally), the only covered lines are class, include Sidekiq::Worker, and two defs. Every method body is 0. The file is completely untested.

The obvious fix does not work

Adding track_files "{app,lib}/**/*.rb" makes it worse — the two environments then disagree on the denominator as well, because SimpleCov's static LinesClassifier counts relevant lines differently than runtime Coverage:

track_files + CI=true   ->  4193 / 4856  (86.35%)   unchanged
track_files + local     ->  3772 / 5367  (70.28%)

I measured the filter options too. Every one leaves local ≠ CI, and filtering spec/ widens the gap (9.2pp → 15.2pp), since spec/ is the one bucket both environments agree on:

Config	eager (CI)	lazy (local)
current	86.35%	95.54%
filter spec/	78.17%	92.64%
rails profile equivalent	77.09%	92.31%

eager_load is the whole story. No SimpleCov setting reconciles it.

The part that actually bites

Eager loading is in CI specifically to catch autoload and NameError breakage. Gating it on CI means that entire class of bug cannot fail locally — only on CI, after a push.

Proposed fix

config.eager_load = true in test, unconditionally. Measured cost: ~0.5s on boot, 2.7s → 3.2s.

Then backfill the coverage it exposes, which is the larger half of the work.

Separately worth deciding, but deliberately not bundled in: SimpleCov.start "rails" would stop the tests grading themselves and report ~77%. That is a policy change that visibly drops the headline number and should be a conscious call, not smuggled in behind a defect fix.

🤖 Generated with Claude Code

Start with config/environments/test.rb and spec/spec_helper.rb, then run the local and CI-style bundle exec rspec commands described in the issue. Review the exposed app files and their coverage before deciding how to backfill tests. Done means local and CI coverage measure the same application scope and the newly exposed untested code is addressed.