gateway-eunit

name	gateway-eunit
description	Run the Yuzu Erlang gateway eunit test suite correctly. Sources the Erlang toolchain, uses --dir to work around rebar3 auto-discovery bug (#337), and explains how to interpret the output. Use when the user asks to run gateway unit tests, verify a gateway change, check for regressions in eunit, or chase an eunit flake.

gateway-eunit

Runbook for exercising the Yuzu Erlang gateway eunit suite.

Command

From the repo root:

source scripts/ensure-erlang.sh >/dev/null && \
  command -v erl >/dev/null || { echo "Erlang missing — check scripts/ensure-erlang.sh output"; exit 1; }
cd gateway && rebar3 eunit --dir apps/yuzu_gw/test

Extra args (e.g. --module yuzu_gw_agent_tests) go on the end. If the user names a specific module, still pass --dir apps/yuzu_gw/test — it is required, not optional.

To capture output without burning tokens, redirect to /tmp/ and tail the result:

rebar3 eunit --dir apps/yuzu_gw/test > /tmp/eunit_run.txt 2>&1; tail -30 /tmp/eunit_run.txt

Why --dir is mandatory

rebar3 3.27 decides "is this test module in the project" by intersecting against the application's compiled modules list in yuzu_gw.app, which only contains src/ modules. Test modules whose name has no 1:1 src/ counterpart (yuzu_gw_circuit_breaker_tests, yuzu_gw_env_override_tests, yuzu_gw_scale_tests, every *_SUITE file, helpers like yuzu_gw_perf_helpers) get rejected before any test runs:

===> Error Running EUnit Tests:
  Module `yuzu_gw_circuit_breaker_nf_tests' not found in project.
  ...

With --dir apps/yuzu_gw/test, rebar3 scans the directory directly and accepts every module. This is tracked as issue #337; the workaround is in tree in scripts/run-tests.sh already.

Interpreting output

• All N tests passed. — clean pass. Current expected total: 148.
• Passed: N. One or more tests were cancelled. — at least one test timed out at the eunit 5-second default. The cancellation usually cancels the entire enclosing {setup, ...} group, so the real impact is larger than "one test". Search for *timed out* in the full output to find the culprit.
• Module X not found in project. — you forgot --dir. See #337 above.
• Stray connection_refused / Failed to notify stream status log lines — fixture leak from a prior test module. Don't ignore; they have caused real test flakes (#336).

--module does NOT give isolation

A common trap: running rebar3 eunit --dir apps/yuzu_gw/test --module yuzu_gw_agent_tests to "isolate" a single module. It does not. rebar3 runs the full suite FIRST (the --dir phase), then the filtered module SECOND, in the same BEAM VM. The second run inherits polluted state (meck mocks, registered names, leaked processes) from the first — so a passing filtered run does not prove the test is order-independent, and a failing one may be failing because of pollution rather than the test itself.

To get real isolation, either:

1. Delete _build/test between runs (rm -rf gateway/_build/test), which forces a fresh BEAM.
2. Spin up erl directly on the compiled beams (erl -pa _build/test/lib/yuzu_gw/ebin -pa _build/test/lib/*/ebin) and run test functions manually — useful for reproducer scripts when bisecting a leak source.

Debugging a hang

If a test times out and fixture state at setup time looks clean, the problem is often a mock process registered under a canonical gen_server name (e.g. yuzu_gw_registry) that silently discards gen_server:call messages. The diagnostic that finds these fast: process_info(Pid, [message_queue_len, status, current_function, current_stacktrace]) on the target pid. Spawn the probe from inside the hanging init/1 via a sleeping helper process so it fires while the call is stuck. This technique found the root cause of #336 when the issue's original hypothesis was wrong.

After any change

Always follow up with rebar3 dialyzer (see the gateway-dialyzer skill). AGENTS.md mandates dialyzer runs after every Erlang change — compilation succeeding is not enough because warnings_as_errors only catches compile warnings, not dialyzer warnings.