container.training/slides/k8s/testing.md

Testing

There are multiple levels of testing:

• unit testing (many small tests that run in isolation),

• integration testing (bigger tests involving multiple components),

• functional or end-to-end testing (even bigger tests involving the whole app).

In this section, we will focus on unit testing, where each test case should (ideally) be completely isolated from other components and system interaction: no real database, no real backend, mocks everywhere.

(For a good discussion on the merits of unit testing, we can read Just Say No to More End-to-End Tests.)

Unfortunately, this ideal scenario is easier said than done ...

---

Multi-stage build

FROM <baseimage>
RUN <install dependencies>
COPY <code>
RUN <build code>
RUN <install test dependencies>
COPY <test data sets and fixtures>
RUN <unit tests>
FROM <baseimage>
RUN <install dependencies>
COPY <code>
RUN <build code>
CMD, EXPOSE ...

• This leverages the Docker cache: it the code doesn't change, the tests don't need to run

• If the tests require a database or other backend, we can use docker build --network

• If the tests fail, the build fails; and no image is generated

---

Docker Compose

version: 3
service:
  project:
    image: my_image_name
    build:
      context: .
      target: dev

  database:
    image: redis
  backend:
    image: backend

docker-compose build && docker-compose run project pytest -v

---

Skaffold/Container-structure-test

• The test field of the skaffold.yaml instructs skaffold to run test against your image.

• It uses the container-structure-test

• It allows to run custom commands

• Unfortunately, nothing to run other Docker images

  (to start a database or a backend that we need to run tests)