What is a pytest fixture and how to use it?

Question

Accepted Answer

**pytest fixture** provides **test setup and teardown** functionality.

```python
import pytest
import tempfile
import os

# Simple fixture
@pytest.fixture
def sample_data():
    return {"users": [{"name": "Alice"}, {"name": "Bob"}]}

def test_user_count(sample_data):
    assert len(sample_data["users"]) == 2

# Fixture with setup/teardown
@pytest.fixture
def temp_file():
    # Setup
    fd, path = tempfile.mkstemp()
    with os.fdopen(fd, "w") as f:
        f.write("test data")

yield path  # Test runs here

# Teardown
    os.unlink(path)

def test_file_content(temp_file):
    with open(temp_file) as f:
        assert f.read() == "test data"

# Fixture scope
@pytest.fixture(scope="module")  # Once per module
def db_connection():
    conn = create_connection()
    yield conn
    conn.close()

@pytest.fixture(scope="session")  # Once per test session
def app():
    return create_app(testing=True)

# Autouse fixture
@pytest.fixture(autouse=True)
def reset_db():
    db.session.begin_nested()
    yield
    db.session.rollback()
```

**Scope options:**
- `function` — per test (default).
- `class` — per test class.
- `module` — per test file.
- `session` — entire test run.

Python: What is a pytest fixture and how to use it?