tests.md

Testing with PyTest

To test an python app is necessary to use some test toll like nose or Pytest. Ins this example we use PyTest for simplicity.

Writting the tests

Pytest searches for tests based on the naming convention in the test files:

1. Test cases are functions with name starting with test_

2. Test files should start with test_

3. Classes with tests should end with _Tests

All test cases should consist at least of an assertion

def test_pass():
    assert True

Configuring PyTest

If you want to use your own name convention or configure other properties you can do it by creating a pytest.ini in the root of the test folder.

In this example I just configure the junit report to generate files in the old format to be used on CI-CD tools

# content of pytest.ini
[pytest]
junit_family=legacy

Test Requirements

Its a good practicie use a exclusive requiremts file for the testing because these tools should not be package together with the application.

So we create a second requirements file in the test folder.

bandit==1.7.0
pylama==7.7.1
pytest==6.2.5
pytest-xdist==2.4.0

The contents of this file are packages used to run the tests (pytest and pytest-xdist) and verify the code (pylama and bandit).

Dockerfile layer

On the Dockerfile we create a new layer reusing the requirement layer and naming it as test. Then we copy the app code, install the test requirements and execute the tests:

WORKDIR /app 

COPY requirements.txt requirements.txt

RUN pip install -r requirements.txt && pip check

FROM requirements as test

COPY src /app

RUN pip install -r /test/requirements.txt

RUN pytest -n 4

The command who execute the tests is

RUN pytest --junit-xml=/reports/unit.xml

It calls the pytest packaging passing the option --junit-xml that generate a report in the given path.

The pytest command searches for python tests and find a simple test we added before.