How to Write a New Unit Test

This project uses pytest as its testing framework. This short guide explains how to add new unit tests so that they are clear, consistent, and easy to maintain.

File Structure

• Unit tests go in tests/<module>, where <module> is the name of a group of related classes or functions. It does not have to match the exact module name, but it should be meaningful and consistent.

• Test data belongs in tests/<module>/data.

Keeping tests organized by feature area makes it easier to navigate the test suite and quickly find related tests.

Guidelines

• Use parametrization with pytest.mark.parametrize to cover multiple inputs and outputs in a single test function. This keeps tests concise, avoids repetition, and makes failures easier to interpret.

• Ensure unique test names or IDs when using parametrization. Pytest automatically generates names, but in some cases they may be too similar. If that happens, provide explicit IDs:

  import pytest
  
  @pytest.mark.parametrize(
      "value, expected",
      [
          pytest.param(1, "one", id="int-1"),
          pytest.param(2, "two", id="int-2"),
      ]
  )
  def test_number_to_string(value, expected):
      assert number_to_string(value) == expected
  

  Alternatively, you can pass an ids list directly:

  @pytest.mark.parametrize(
      "value",
      [1, 2, 3],
      ids=["case-1", "case-2", "case-3"]
  )
  def test_is_positive(value):
      assert is_positive(value)
  

• Test IDs do not need to be creative. In doubt, simply use a sequential numbering scheme like case-1, case-2, etc.

Readable test names make failures much easier to diagnose, especially when running large test suites.