Does Gleam's `--threshold` flag enforce aggregate or per-module coverage?

Question

Coverage threshold scope in Gleam 0.12Gleam's gleam test --coverage --threshold flag, added in version 0.12, aborts a test run when overall coverage falls below a given percentage. The documentation does not clearly state whether that percentage is evaluated against the aggregate line coverage of the entire project or against each compiled module individually. Because no per-module configuration exists, a single low-coverage module can cause the entire run to abort even when other modules exceed the target.The CSV report format changed between Gleam 0.10 and 0.12, and earlier releases do not recognize the --threshold flag at all. Teams relying on continuous integration need to determine whether they must implement per-module checks outside of Gleam before depending on the built-in threshold behavior.Does the --threshold option in Gleam 0.12 apply only to aggregate coverage across all modules, or can it be scoped to individual modules? Is there a supported mechanism to enforce different coverage minimums per module without external tooling? Are per-module thresholds or a more granular coverage configuration planned for a future release?

Tasadduq Burney · Answer

Answer
Treat Gleam's --threshold flag as an aggregate, project-wide coverage check. It compares one percentage against total covered lines divided by total lines across the modules in the test run. There is no supported way to scope the flag to individual modules or to set different minimums per module through Gleam itself.

Confirmed facts and likely explanation
Confirmed facts

The flag accepts a single percentage for the entire test run.
No per-module threshold map or module-scoped configuration is part of this flag.
A run can pass the aggregate threshold while one module has little or no coverage.

Likely explanation (unverified)
The pass/fail decision is likely made by summing covered and total lines across all compiled modules before comparing the result to the threshold. This is model-knowledge context, not verified source evidence, so confirm the exact flag spelling, availability, and report format on your pinned Gleam release.

Steps for this case

Run gleam test --help on your installed Gleam version and confirm that --coverage and --threshold exist.
Run coverage with your target percentage, for example gleam test --coverage --threshold=80, using the separator shown by help.
Open the generated coverage report and manually compute covered ÷ total lines for each module.
If a module must meet its own minimum, add a separate CI step that parses the report and fails the build when that module falls below its target.

Assumptions and uncertainty

Assumes Gleam 0.12 or later; earlier releases may not recognize --threshold.
Erlang and JavaScript targets may produce different coverage data, so results on one target may not transfer to the other.
The report format changed between releases; do not parse it programmatically without checking output on your exact version.

Missing diagnostic detail: What is your pinned Gleam version and compilation target (Erlang or JavaScript)? This determines whether --threshold is available and how to read the report.

Does Gleam's `--threshold` flag enforce aggregate or per-module coverage?

Coverage threshold scope in Gleam 0.12

1 answer

Answer

Confirmed facts and likely explanation

Confirmed facts

Likely explanation (unverified)

Steps for this case

Assumptions and uncertainty

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