Concept

Test fixtures

A fixture builds something tests need, such as a temporary file or a prepared object, and hands it to each test that asks for it by name. Built-in ones like tmp_path cover the common cases.

What a session covers

The tutor works through these with you, in conversation and code. A session ends when you have shown them, not when a video does.

Explain what a fixture provides and how a test asks for one
Write a fixture that builds a prepared object for several tests
Use tmp_path to test code that reads and writes files

In practice

A few lines that show Test fixtures doing its job.

Python

import pytest
from store import Store

@pytest.fixture
def store(tmp_path):
    return Store(tmp_path / "data.json")

def test_saves_and_loads(store):
    store.put("a", 1)
    assert store.get("a") == 1

def test_starts_empty(store):
    assert store.get("a") is None

The common mistake

Watch for

Sharing one mutable object across tests through a module-level variable. Tests then depend on the order they run in, and a failure in one shows up in another.

What to know first

Your roadmap puts these before Test fixtures, unless you already know them.

Writing tests with pytest

How it stays learned

Once a session shows you understand Test fixtures, it comes back for review. Each review takes a minute and tells the memory model how well you still know it.

Day 3First recall, while it is fresh
Day 7Second, a week on
Day 18Last, when it has settled

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