[BUG] --coverage reports 0% for contract/library source when tests live in the recommended separate test crate

[shiqicao]

Summary

The docs tell us to keep all #[test] functions in a dedicated test crate, and aztec test warns when tests are found in a contract crate. But --coverage only attributes execution to files of the crate directly under test, so a project laid out the recommended way reports 0% for every contract and library file it owns — no matter how thorough its tests are.

The two pieces of guidance are mutually exclusive today, and there's no documented way to satisfy both:

• Follow "keep tests in the test crate" → your contract/library source is never attributed → permanently 0%.
• Get a real number → tests must be co-located in the crate under test → warning, unnecessary recompilation, and test source embedded in the shipped artifact (below).

From the docs (Keep tests in the test crate):

Keep all #[test] functions in the test crate, not in the contract crate.

and errors/1:

WARNING: Found tests in contract crate(s): … Tests should be in a dedicated test crate, not in the contract crate.

Environment

• aztec 5.0.1, bundled nargo 1.0.0-beta.22 (noirc 1.0.0-beta.22+c57152f91260ecdb9faad4efc20abb14b6d2ece7)
• Command: aztec test --coverage on a workspace of X / X_test pairs

Reproduction

A workspace laid out exactly as the docs recommend:

Nargo.toml                   # workspace members: common, common_test, …
common/                      # type = "lib"      — library under test, no #[test] fns
common_test/                 # type = "lib"      — deps: common; contains all #[test] fns
token_bridge_contract/       # type = "contract" — no #[test] fns
token_bridge_contract_test/  # type = "lib"      — deps: token_bridge_contract; all #[test] fns

Run aztec test --coverage, then inspect target/coverage/<package>/lcov.info.

Observed:

1. target/coverage/common_test/lcov.info emits SF: entries only for its own common_test/src/*_test.nr files. It never emits an SF: for common/src/*.nr, although every one of those files is exercised by those tests.
2. target/coverage/common/lcov.info does list all 7 common/src/*.nr files — with all 155 instrumented lines at zero hits.
3. Every production contract reads 0%: token_bridge_contract/src/main.nr 0/147, token_vault_bridge_contract/src/main.nr 0/203, and so on.

This is about placement, not test quality. We took an existing test out of common_test/src/packable_bounded_vec_test.nr and put an equivalent mod test inside common/src/packable_bounded_vec.nr — same assertions, no new logic. That file went from 0% to 97% (32/33 lines).

Cause

The evaluation tracker is narrowed to the crate under test (tooling/nargo_cli/src/cli/test_cmd.rs#L690-L693):

if let Some(evaluation_tracker) = context.evaluation_tracker.as_mut() {
    let crate_files = context.def_maps[&crate_id].file_ids();
    evaluation_tracker.restrict_to_files(&crate_files);
}

and the baseline is built from the same set (test_cmd/coverage.rs#L22-L41):

let def_map = &context.def_maps[&crate_id];
let allowed_files = def_map.file_ids();

So a separate X_test package — the documented layout — can never contribute coverage to X's source.

Why co-locating tests isn't an acceptable workaround

Beyond the recompilation reason the docs give, co-located test source is embedded in the compiled artifact's file_map, including on a production aztec-nargo compile. functions/bytecode stay clean, so there's no circuit or ABI impact — but file_map is the largest section of the artifact (~810KB of a ~994KB contract JSON in our case), and projects that publish their contracts as an npm package ship those target/*.json files to consumers. So co-locating means shipping test source downstream.

It also wouldn't actually work for TXE tests: see #24987 — under --coverage, oracle-calling tests are skipped entirely, so co-locating them yields no coverage either.

Ask

1. Attribute coverage across workspace path dependencies: when a test in crate B executes code from A (a path dependency in the same workspace), count it toward A's source, the way cargo llvm-cov and gcov-based tooling do — ideally keyed by executed source location rather than package ownership.
2. Or add an opt-in flag (--coverage-include-deps / --coverage-workspace) that widens instrumentation to workspace path dependencies.
3. Failing either, please document how a project that follows "Keep tests in the test crate" is supposed to obtain coverage for its own contract and library code. As written, the testing-layout guidance and the --coverage feature contradict each other, and we'd rather not build a workaround around a gap you intend to close.

Note: --coverage is implemented in Noir (nargo test --coverage), so the fix may belong in noir-lang/noir. Filing here because the test-layout recommendation is Aztec's and aztec test is the documented entry point — happy to re-file upstream if you prefer.

Related: #24987 (--coverage silently skips oracle-calling tests and still reports them as passed).