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Writing KUTTL test for an operator

Kuttl is a tool for testing Kubernetes operators. Each kuttl test suite consists of a series of test steps that might modify the state of the cluster or check its state. A kuttl test step will use all yaml files that begin with its numeric index. For example, if we had a file 00-deploy.yaml and a 00-assert.yaml, kuttl would apply the changes described by the file 00-deploy.yaml and then wait until the state of the cluster matches the one found in 00-assert.yaml. If it's found, then the step is successful. If after the timeout, the state of the cluster does not match the assert, then the test fails. Kuttl also supports errors files, which will check that the cluster does not match the state described in the file (i.e tha inverse of an assert file).

What should be tested for in a kuttl suite depends on the details of the operator itself. A good place to find more information is the controller.go file for the operator, there you should find hints on what resources does the operator create and/or manage. Another source of information s the operator API where it list which attributes the operator exposes. As an example, in keystone, one can find here the properties of the API. Another good option would be to contact the people listed as approvers in the operator's OWNERS file. Below are some example of things to assert while writing the tests (they might not apply to all operators):

  • Creation (the operator should deploy properly the service in question)
  • Scale up and down (the operator should control properly the number of replicas in the deployment and create and destroy pods as needed)
  • Destroy (the operator should delete properly the resources deployed)
  • Update (the operator applies some change to the resources deployed). As an example, the keystone-operator can change the configuration of the keystone service, which entails deleting the keystone pod and creating a new one with the modified configuration.

Below are some conventions that are assumed for kuttl tests in openstack-k8s-operators:

  • There should be a kuttl-test.yaml file at the root of the operator repo which contains the kuttl configuration.
  • There should be ${OPERATOR_NAME}_kuttl and ${OPERATOR_NAME}_kuttl_run targets in install_yamls. The first will install all dependencies, run the tests and cleanup, while the latter will simply run the tests, without further modifying the environment.
  • There should be an assert file under operator-path/tests/kuttl/common/assert_sample_deployment.yaml. This assert file should be used to validate the deployment of the operator. In parallel, a target called ${OPERATOR_NAME}_deploy_validate should be added to install_yamls. This new target should use a kuttl assert command to check the validity of the operator deployment against the assert_sample_deployment.yaml assert.

Below are some things to keep in mind while writing kuttl tests:

  • Scripting can be used in assert files (useful if for example want to check some parameter using regex, since that is not supported by kuttl). As mentioned in the kuttl docs, the scripts used in an assert are passed to sh -c  to be run, so the result can be environment dependent. For example, sh is often symlinked to bash, but in many environments this will not be true, so be careful to not use bash (or other shell) specific features.

  • If you execute some oc command in a script, you'll need to pass -n openstack  since the namespace is not gathered from the kuttl configuration for scripts (the namespace is gathered for the yaml section of the assert if the namespaced option is set to True in the kuttl configuration).

  • Individual assert files can be applied using the kubectl-kuttl assert command. This is useful to apply manually some changes to the cluster and debug the assert file without needing to run the whole test suite. Example usage:

kubectl-kuttl assert --namespace openstack /path/to/02-assert.yaml --timeout 10.

Note that the assert command does not support having TestAssert blocks in the assert files (kudobuilder/kuttl#221).

  • There is also an errors command to debug errors files.

Tips and common mistakes

  • In a test step file you can create, update, delete multiple resources just separate them with ---.

  • If you update an existing resource in a test step file you only need to provide the fields that you want to change, kuttl will merge patch the existing resource.

  • You can use the TestStep in a test step file to execute a script to do complex changes in the cluster. However TestSteps and other resource definitions within the same test step file is applied in an random order by kuttl. If you need a well defined sequence of steps then you need to use separate step files with increasing indexes.

  • In an assert file you can match multiple resources, just separate them with ---.

  • The expected resource state in an assert file does not have to list all the fields of the resource type. The fields that are not listed in the assert file will be ignored during matching with the real resource. This way you can assert only the fields relevant to the given test case.

  • You can use the TestAssert resource in an assert or error file to run shell scripts to assert complex things. However only a single TestAssert can be used per file. If you add multiple TestAsserts then only the last one will be executed and the rest is ignored by kuttl.

  • If you use scripts in TestStep or TestAssert then add set -euxo pipefail to the start of the script to ensure that no error is ignored.