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.

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.
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.

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