Write integration tests for your charm

From Zero to Hero: Write your first Kubernetes charm > Write integration tests for your charm

See previous: Write scenario tests for your charm

This document is part of a series, and we recommend you follow it in sequence. However, you can also jump straight in by checking out the code from the previous branches:

git clone https://github.com/canonical/juju-sdk-tutorial-k8s.git
cd juju-sdk-tutorial-k8s
git checkout 09_scenario_test
git checkout -b 10_integration_testing

A charm should function correctly not just in a mocked environment but also in a real deployment.

For example, it should be able to pack, deploy, and integrate without throwing exceptions or getting stuck in a waiting or a blocked status – that is, it should correctly reach a status of active or idle.

You can ensure this by writing integration tests for your charm. In the charming world, these are usually written with pytest-operator library.

In this chapter you will write two small integration tests – one to check that the charm packs and deploys correctly and one to check that the charm integrates successfully with the PostgreSQL database.


  1. Prepare your test environment
  2. Prepare your test directory
  3. Write and run a pack-and-deploy integration test
  4. Write and run an integrate-with-database integration test
  5. Review the final code

Prepare your test environment

In your tox.ini file, add the following new environment:

description = Run integration tests
deps =
    -r {tox_root}/requirements.txt
commands =
    pytest -v \
           -s \
           --tb native \
           --log-cli-level=INFO \
           {posargs} \

Prepare your test directory

Create a tests/integration directory:

mkdir ~/fastapi-demo/tests/integration

Write and run a pack-and-deploy integration test

Let’s begin with the simplest possible integration test, a smoke test. This test will build and deploy the charm and verify that the installation hooks finish without any error.

In your tests/integration directory, create a file test_charm.py and add the following test case:

import asyncio
import logging
from pathlib import Path

import pytest
import yaml
from pytest_operator.plugin import OpsTest

logger = logging.getLogger(__name__)

METADATA = yaml.safe_load(Path("./metadata.yaml").read_text())

async def test_build_and_deploy(ops_test: OpsTest):
    """Build the charm-under-test and deploy it.

    Assert on the unit status before any relations/configurations take place.
    # Build and deploy charm from local source folder
    charm = await ops_test.build_charm(".")
    resources = {
        "demo-server-image": METADATA["resources"]["demo-server-image"][

    # Deploy the charm and wait for waiting/idle status
    # The app will not be in active status as this requires a database relation
    await asyncio.gather(
        ops_test.model.deploy(charm, resources=resources, application_name=APP_NAME),
            apps=[APP_NAME], status="waiting", raise_on_blocked=True, timeout=1000

In your Multipass Ubuntu VM, run the test:

tox -e integration

The test takes some time to run as the pytest-operator running in the background will add a new model to an existing cluster (whose presence it assumes). If successful, it’ll verify that your charm can pack and deploy as expected.

Write and run an integrate-with-database integration test

The charm requires a database to be functional. Let’s verify that this behavior works as intended. For that, we need to deploy a database to the test cluster and integrate both applications. Finally, we should check that the charm reports an active status.

In your tests/integration/test_charm.py file add the following test case:

async def test_database_integration(ops_test: OpsTest):
    """Verify that the charm integrates with the database.

    Assert that the charm is active if the integration is established.
    await ops_test.model.deploy(
    await ops_test.model.integrate(f"{APP_NAME}", "postgresql-k8s")
    await ops_test.model.wait_for_idle(
        apps=[APP_NAME], status="active", raise_on_blocked=True, timeout=1000

But if you run the one and then the other (as separate pytest ... invocations, then two separate models will be created unless you pass --model=some-existing-model to inform pytest-operator to use a model you provide.

In your Multipass Ubuntu VM, run the test again:

ubuntu@charm-dev:~/fastapi-demo$ tox -e integration

The test may again take some time to run.

Pro tip: To make things faster, use the --model=<existing model name> to inform pytest-operator to use the model it has created for the first test. Otherwise, charmers often have a way to cache their pack or deploy results; an example is https://github.com/canonical/spellbook .

When it’s done, the output should show two passing tests:

  demo-api-charm/0 [idle] waiting: Waiting for database relation
INFO     juju.model:model.py:2759 Waiting for model:
  demo-api-charm/0 [idle] active: 
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- live log teardown --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
INFO     pytest_operator.plugin:plugin.py:783 Model status:

Model            Controller       Cloud/Region        Version  SLA          Timestamp
test-charm-2ara  main-controller  microk8s/localhost  3.1.5    unsupported  09:45:56+02:00

App             Version  Status  Scale  Charm           Channel    Rev  Address        Exposed  Message
demo-api-charm  1.0.0    active      1  demo-api-charm               0  no       
postgresql-k8s  14.7     active      1  postgresql-k8s  14/stable   73  no       

Unit               Workload  Agent  Address       Ports  Message
demo-api-charm/0*  active    idle          
postgresql-k8s/0*  active    idle         

INFO     pytest_operator.plugin:plugin.py:789 Juju error logs:

INFO     pytest_operator.plugin:plugin.py:877 Resetting model test-charm-2ara...
INFO     pytest_operator.plugin:plugin.py:866    Destroying applications demo-api-charm
INFO     pytest_operator.plugin:plugin.py:866    Destroying applications postgresql-k8s
INFO     pytest_operator.plugin:plugin.py:882 Not waiting on reset to complete.
INFO     pytest_operator.plugin:plugin.py:855 Forgetting main...

========================================================================================================================================================================== 2 passed in 290.23s (0:04:50) ==========================================================================================================================================================================
  integration: OK (291.01=setup[0.04]+cmd[290.97] seconds)
  congratulations :) (291.05 seconds)

Congratulations, with this integration test you have verified that your charms relation to PostgreSQL works as well!

Review the final code

For the full code see: 10_integration_testing

For a comparative view of the code before and after this doc see: Comparison

See next: Open a Kubernetes port in your charm

Contributors: @bschimke95

Last updated 6 days ago.