matrix-docker-ansible-deploy/docs/molecule-testing.md

Molecule testing for roles

Roles in roles/custom/ can carry a Molecule scenario, which installs the role into a container and then checks that the component actually came up with the configuration the role rendered.

Not every role has one yet. Roles without a scenario are simply not tested.

Running a scenario

just molecule                                    # list roles that have a scenario
just molecule matrix-alertmanager-receiver       # run one
just molecule matrix-alertmanager-receiver converge   # any molecule subcommand

The first run creates a virtualenv in var/molecule-venv/ (gitignored) from molecule-shared/requirements.txt. Docker must be working, and a run takes minutes because it pulls container images.

MOLECULE_DISTRO selects the base image; it defaults to ubuntu2604.

Molecule is deliberately not part of the prek hooks. A run is far too slow to sit in front of a commit, and it needs Docker. Run it when you have touched a role; CI runs it too, asynchronously.

What CI runs

.github/workflows/molecule.yml does not run every scenario on every push — with one repository holding every role, that would be unaffordable. Its first job works out which roles the push actually touched, keeps the ones that have a scenario, and builds the job matrix from those. A documentation change runs nothing.

When the diff base cannot be determined (a new branch, a force push), it falls back to running every scenario, which errs toward testing too much rather than too little. workflow_dispatch accepts an optional role name.

Automerge

A role that has a scenario is listed in the Molecule automerge rule in .github/renovate.json, so patch bumps of its component merge on their own once the scenario has passed on them.

Add your role to that list when you add its scenario. bin/check-molecule-automerge-list.py runs from prek and fails the commit if the list and the scenarios have drifted apart. The direction that matters is a role staying in the list after losing its scenario, since its bumps would then merge with nothing exercising them.

Writing a scenario

Start from roles/custom/matrix-alertmanager-receiver/molecule/default/ — it is the reference. Four things differ from a standalone role’s scenario, all of them consequences of these roles living inside a playbook:

The playbook’s context has to be supplied

The role reads variables that matrix-base and group_vars/matrix_servers would normally provide. The set is small — matrix_base_data_path, matrix_domain, matrix_user_name, matrix_group_name, matrix_user_uid, matrix_user_gid — and belongs in the scenario’s group_vars, rather than including matrix-base, which does much more than a role scenario needs.

The matrix user and group must exist first

The roles’ file tasks set owner: and group: by name, and Ansible resolves those through the passwd database, so prepare.yml has to create them before the role runs.

Most components need a homeserver to be present

Many of these components contact the homeserver while starting up, and exit if it is unreachable — matrix-alertmanager-receiver, for example, fetches /_matrix/client/v3/joined_rooms to resolve its room mapping and exits with a failure if that call fails.

A stub is enough, and is what the reference scenario stands up. The point of these scenarios is to prove that the component starts and does not choke on the configuration the role rendered — not to exercise real bridging. A scenario should never need a credential or an account on a third-party network; that is the line where it stops being a test of this repository.

verify.yml is a separate play

Role defaults are out of scope there, so any path it reads has to be pinned in the scenario’s group_vars. Deliberately do not pin the component’s version that way: read it from the role’s defaults/main.yml with include_vars, so the assertion compares the running image against what the role ships rather than against the scenario itself.

Shared files

molecule-shared/ holds what would otherwise be duplicated into every role:

• requirements.txt — the Python packages, for both CI and just molecule.
• requirements.yml — the external Ansible roles and collections the scenarios need. Each scenario symlinks its own molecule/default/requirements.yml at this file: Molecule checks for a requirements file at that default path before it will install anything, so pointing at the shared one through requirements-file alone is silently ignored.
• vars.yml — helper container images used for probing, pinned once. They carry # renovate: annotations and a custom manager in .github/renovate.json keeps them current.

A helper image is used to reach a role’s container over its own container network. That indirection is deliberate: the roles publish no host port, matching a real deployment, and publishing one for the test would collide between scenarios running in parallel.

Making a scenario worth having

A suite that only waits for the systemd unit to become active proves very little: these units carry Restart=always, so a container crash-looping on a bad configuration still reports active. Check the restart counter alongside it, and probe something the component can only answer correctly if the role’s configuration reached it.

Give the scenario values that differ from both the role’s defaults and the component’s own defaults. Otherwise a passing assertion cannot distinguish “the role configured this” from “it would have happened anyway”.

Then try to break it. If a scenario cannot be made to fail by deliberately breaking the thing it checks, it is not testing that thing.

Falsify every assertion, not just enough of them to see the scenario go red. An assertion that passes is not necessarily an assertion that works: one control here asserted that a component emitted no DEBUG records from a particular module, and it passed just as happily with that module set to debug, because the module emits none on a first run either way. It was green for the wrong reason, and only breaking it deliberately exposed that.

Two traps make a falsification pass when it should fail:

• molecule converge against an already-running instance rewrites the configuration but only does state: started, so the container keeps the old one. Full molecule test is unaffected - this bites the local iterate-with-converge loop, which is where falsifications get run.
• The failure must land on the assertion you aimed at. If it fails at an earlier gate, you have proved something about that gate instead.

Work out whether the component crashes or retries

Some components exit when their configuration is wrong; others catch everything and retry forever. For the second kind, ActiveState == active and NRestarts == 0 both stay true while the component is completely broken - matrix-reminder-bot and baibot both behave this way, retrying a failed login or profile step indefinitely. There the unit assertions prove nothing on their own, and something the component says about itself has to carry the scenario.

Establish which kind yours is before deciding what the weight-bearing assertion is.

Reading the journal

Grep the whole journal rather than tailing it. Startup lines are the oldest entries, and a component that syncs can bury them under thousands of lines within a minute, so --lines=N loses exactly what you were looking for. Strip ANSI escapes too - some components colour their output, and a plain substring match against raw journal text then fails silently.

Assert against parsed documents

Where a scenario reads a rendered configuration, parse it and assert on the structure rather than matching substrings. A value landing under the wrong key cannot then pass.

Running more than one scenario at once

bin/molecule.sh points ANSIBLE_HOME at var/molecule-ansible-home/<role>/, so each role gets its own copy of the Galaxy collections and roles.

This is not an optimisation - it is a correctness fix. Scenarios install their dependencies with force: true, so two runs sharing ~/.ansible re-extract the same collections underneath each other. The symptom is a collection that was working moments earlier going missing mid-play:

the connection plugin 'community.docker.docker' was not found

If you see that, a concurrent run took the collection out from under you.

ANSIBLE_HOME is left alone if you have already set it, and is unset in CI - each role runs in its own job there, so there is nothing to collide with.

The directories are disposable; var/ is gitignored. Delete var/molecule-ansible-home/ to force a fresh install.

Databases

Scenarios for roles that have a database run against Postgres, not sqlite.

That is what group_vars/matrix_servers selects whenever postgres is enabled, which is the default, so it is what essentially every deployment runs. sqlite is a path almost nobody is on: a bug that stopped the mautrix-meta bridges from starting at all under sqlite sat unreported for a long time, which says plainly enough whose path is worth testing.

molecule-shared/tasks/postgres.yml stands one up on the scenario’s container network. Include it from prepare.yml and point the role at it with its own _database_engine, _database_hostname and credentials. Give the database and user names that differ from the role’s defaults - then the component reaching the database at all proves the role built its connection string out of them.

The image is pinned in molecule-shared/vars.yml at the major the postgres role deploys to new installations, and Renovate carries it forward. When a new major lands, the PR bumping that pin runs every scenario against it, which is the earliest warning we get that a component does not cope with it.

Prefer asserting on the schema the component created over a file on disk: tables can only appear once it has resolved the hostname, authenticated, and run its migrations.

Reclaiming the disk space

just molecule-clean removes what the runs leave under var/.

Two things live there. The per-role Ansible homes are ~7 MB each, rewritten on every run rather than grown, so they are bounded by the number of roles that have a scenario. The shared virtualenv is the bulk of it, over 500 MB, and is recreated on the next run at the cost of a pip install.

--idle-days N restricts it to what has not been touched in N days, which is what makes it safe to run unattended. --yes skips the confirmation.