Tutorial: Writing Commodore Component Tests

This tutorial covers the topic of writing tests for your new or existing Commodore Component. It assumes that you are familiar with writing Commodore Components. If not, see Writing your First Commodore Component.

Currently, we can test components with two approaches:

  1. Unit tests with Go. Easy to understand and write if you are already a Go developer.

  2. Policy tests with Conftest. Uses the Rego syntax from OpenPolicyAgent.

It is up to you to decide which test framework you want to use. Some tests are simpler to do in Go, some are simpler in Rego. A combination of both will combine their advantages.

The policy tests run with the Conftest tool, but for the purpose of this tutorial we will refer to the Rego language, as the policies are written in that syntax.


This tutorial was written on a Linux system.
  1. Go version 1.15, developer environment with Go modules enabled.

  2. docker version 19

Setting up test infrastructure with Go

We’ll start with Go. Create the following directory structure:

├── tests
│   ├── test.yml
│   └── unit
│       ├── defaults_test.go
│       ├── go.mod
│       └── go.sum

The go.mod and go.sum files are created when executing go mod init inside test/unit/. Since we are only creating test code and not an actual Go binary, all Go test files have to end with _test.go. tests/test.yml is sometimes used by components to override values that would only be needed by Commodore when compiling whole catalogs, you can leave it empty for now. We will now start writing the first tests in defaults_test.go.

Writing unit tests with Go

If you are already a Go developer, these should look fairly familiar to you. We will showcase the tests with the Espejo component. If you have component-somename, then leave out component-.

package main

import (

var (
	testPath = "../../compiled/espejo/espejo"

func Test_Deployment_DefaultParameters(t *testing.T) {

	subject := DecodeDeployment(t, testPath+"/10_deployment.yaml")
	require.NotEmpty(t, subject.Spec.Template.Spec.Containers)
	container := subject.Spec.Template.Spec.Containers[0]

	assert.Equal(t, "espejo", container.Name)
	assert.Contains(t, container.Args, "--verbose=false")
	assert.Contains(t, container.Args, "--reconcile-interval=10m")
	assert.Contains(t, container.Args, "--metrics-addr=:8080")
	assert.Contains(t, container.Args, "--enable-leader-election=true")

	require.NotEmpty(t, container.Env)
	env := container.Env[0]
	assert.Equal(t, "WATCH_NAMESPACE", env.Name)
	assert.Equal(t, "metadata.namespace", env.ValueFrom.FieldRef.FieldPath)

func Test_Namespace(t *testing.T) {

	subject := DecodeNamespace(t, testPath+"/01_namespace.yaml")

	assert.Equal(t, "syn-espejo", subject.Name)
	assert.Contains(t, subject.Labels, "name")
We have not yet built a library to host the boilerplate code and common functions.

As you can see, it’s pretty straight forward:

  1. First, load the pre-compiled YAML file into a Go K8s struct that we all know and love

  2. Then, we verify if the values were parsed correctly, using any assertion library of your choice.

To actually run our unit test case, we need to run a Commodore Component compilation first:

COMPONENT_NAME=$(basename ${PWD} | sed s/component-//)
DOCKER_CMD() {docker run --rm --user "$(id -u)" -v "${PWD}:/${COMPONENT_NAME}" --workdir /${COMPONENT_NAME} $*}
DOCKER_CMD --entrypoint /usr/local/bin/jb projectsyn/commodore:latest install
DOCKER_CMD projectsyn/commodore:latest component compile . -f tests/test.yml

Running the tests could look like this:

$ pushd tests/unit > /dev/null && go test -v ./... && popd > /dev/null
=== RUN   Test_Deployment_DefaultParameters
--- PASS: Test_Deployment_DefaultParameters (0.01s)
=== RUN   Test_Namespace
--- PASS: Test_Namespace (0.00s)
ok  	github.com/projectsyn/component-espejo

Writing policy tests with Rego

Some tests are easier to write in Rego than Go unit tests. Consider the following use case: We want to ensure that all generated manifests have a certain label.

With Go unit tests, we would have to

  1. Recursively parse all YAML files

  2. Decode the YAML files into generic objects, so that we can access .metadata.labels

  3. Assert that the desired label is there.

With Rego, this particular test is relatively easy:

recommended_labels {

warn_labels[msg] {
  input.kind != "CustomResourceDefinition"
  not recommended_labels

  msg = sprintf("%s/%s has not recommended labels", [input.kind, name])

Let’s break down the structure:

  1. recommended_labels is an object that verifies that .metadata.labels contain the desired label keys.

  2. warn_labels[msg] is a Rule. If all expressions in the brackets match (including msg), this Rule is considered true.

  3. Since the prefix of the rule is warn_, it will only print a Warning message if there is an object that matches the rule. With deny_, it would fail the test.

Rego (like Datalog and its ancestor Prolog) is declarative. The lines within a rule are not evaluated imperatively. It is important to keep that in mind when writing rules, as it can cause many headaches.

Let’s translate the example to English:

  1. In recommended_labels, we will test whether the Kubernetes object (named input) contains "app.kubernetes.io/managed-by" in the .metadata.labels dictionary. We ignore the actual value here. Since recommended_labels is not a rule, it’s not yet used.

  2. When conftest matches an Object against the rule warn_labels, all expressions in the rule have to evaluate True.

  3. If we pass a CRD, the result of the rule is False because of input.kind != "CustomResourceDefinition", thus the rule does not match, and the test passes.

  4. If we pass a Deployment, we have at least input.kind != "CustomResourceDefinition" that equals to True, but remember, all expressions have to be evaluated.

  5. The other expression, not recommended_labels checks if the object is missing the desired labels. If the given Deployment has the labels, it will fail the rule and pass the test. A Deployment that doesn’t have the labels would match the rule, and thus fail the test.

  6. By now the rule would already match with a Deployment without the labels, and thus fail the test, but we want to give a reason why. As the final expression, we will assign the msg variable a human readable message why the rule matches. Remember, this line can also be the first one since the execution order is determined by Rego and not line by line.

If we now also pass a Namespace or Service objects, the same rules can be applied, since all these objects share the common property .metadata.labels.

If we want to check whether a Namespace has the correct name, this could look like this:

deny_namespace[msg] {
  input.kind = "Namespace"
  ns := "syn-espejo"
  not input.metadata.name = ns

  msg = sprintf("Namespace is not %s", [ns])

In this example, we are using the variable ns to not repeat ourselves. The expression not input.metadata.name = "syn-espejo" is equivalent, but we want to reduce code duplication in the msg expression.

Running the policies could look like this:

$ DOCKER_CMD --volume "${PWD}/tests/policies:/policy" openpolicyagent/conftest:latest test --policy /policy $(find . -type f -wholename "./compiled/${COMPONENT_NAME}/*.yaml")
WARN - ./compiled/espejo/espejo/05_rbac.yaml - ClusterRole/syn-espejo has not recommended labels
WARN - ./compiled/espejo/espejo/05_rbac.yaml - ServiceAccount/espejo has not recommended labels
WARN - ./compiled/espejo/espejo/05_rbac.yaml - ClusterRoleBinding/syn-espejo has not recommended labels
WARN - ./compiled/espejo/espejo/01_namespace.yaml - Namespace/syn-espejo has not recommended labels

14 tests, 10 passed, 4 warnings, 0 failures, 0 exceptions

Run all tests

You could declare all the test commands in the Makefile. Have a look at Component-Espejo for an example. This should also help running tests in any CI/CD pipelines, such as GitHub Actions.


I hope this guide has shown how we can test our component without having to compile a whole catalog and applying it to a cluster.

At the moment, we are limited to only have tests against a single compilation (e.g. the default parameters). Later on, we want to enable testing different parameter sets.