Pytest Fixtures

Fixture management and conftest.py design for Python test suites.

When to Use

•Creating new test directories
•Refactoring test fixtures
•Reviewing tests for DRY violations
•Planning fixture hierarchy

MCP Workflow

python

# 1. Find existing conftest files
serena.search_for_pattern("conftest\\.py", paths_include_glob="**/tests/**")

# 2. Identify fixture definitions
serena.search_for_pattern("@pytest\\.fixture", paths_include_glob="**/tests/**")

# 3. Find duplicate fixture names
jetbrains.search_in_files_by_text("def sample_", fileMask="test_*.py")

# 4. Check existing helpers
serena.get_symbols_overview(relative_path="tests/")

Fixture Hierarchy

code

tests/
├── conftest.py           # Shared across ALL tests
│   └── Fixtures: session-scoped, DB connections, API clients
├── cli/
│   ├── conftest.py       # CLI-specific fixtures
│   │   └── Fixtures: CLI runner, mock console, sample paths
│   └── test_*.py
└── core/
    ├── conftest.py       # Core-specific fixtures
    │   └── Fixtures: domain models, sample data
    └── {module}/
        ├── conftest.py   # Module-specific (rarely needed)
        └── test_*.py

Scope Selection Guide

Scope	Recreated	Use When
`function`	Each test	Default; mutable state
`class`	Each class	Class-based tests, shared setup
`module`	Each file	Expensive setup, immutable data
`session`	Once	DB connections, API clients

Rule: Start with function, widen scope only for performance.

Fixture Design Patterns

1. Factory Fixture (Preferred for Flexibility)

python

@pytest.fixture
def make_user():
    """Factory that creates users with custom attributes."""
    def _make_user(name: str = "test", role: str = "user") -> User:
        return User(name=name, role=role)
    return _make_user

# Usage in test
def test_admin_access(make_user):
    admin = make_user(role="admin")
    assert admin.can_access_admin_panel()

2. Parameterized Fixture

python

@pytest.fixture(params=["sqlite", "postgres", "mysql"])
def database(request):
    """Runs test with each database type."""
    return create_connection(request.param)

3. Cleanup Fixture (yield pattern)

python

@pytest.fixture
def temp_file(tmp_path):
    """Provides temp file and cleans up after test."""
    path = tmp_path / "test.txt"
    path.write_text("content")
    yield path
    # Cleanup happens after test

Duplicate Detection Checklist

Run before creating fixtures:

bash

# Find fixtures with same name
grep -r "@pytest.fixture" tests/ | grep "def " | cut -d: -f2 | sort | uniq -d

# Find common helper patterns
grep -rh "def get_output\|def create_\|def make_\|def sample_" tests/

conftest.py Planning

Before Creating New Test Directory

•Check parent conftest - What fixtures already exist?
•Identify shared fixtures - What 2+ tests need?
•Plan fixture scope - Function/module/session?
•Document dependencies - What does each fixture need?

conftest.py Template

python

"""
Fixtures for {directory} tests.

Shared fixtures:
- {fixture_name}: {description}

Dependencies:
- Uses: {parent_fixture} from parent conftest
"""
import pytest

@pytest.fixture
def fixture_name():
    """One-line description."""
    return value

DRY Violation Patterns

Pattern	Problem	Solution
Same fixture in 2+ files	Maintenance burden	Move to shared conftest
`get_output()` in multiple files	Helper duplication	Create `helpers.py`
Copy-paste setup code	Test fragility	Factory fixture
Inline data creation	Readability	Data fixtures

Helper Function Consolidation

code

tests/
├── conftest.py       # Fixtures only
├── helpers.py        # Shared utility functions
│   ├── get_output()
│   ├── assert_table_contains()
│   └── create_mock_response()
└── fixtures/         # Complex fixture data
    ├── sample_metrics.json
    └── sample_datasets.yaml

Output Format

markdown

## Fixture Analysis: {directory}

### Existing Fixtures
| Location | Fixture | Scope | Used By |
|----------|---------|-------|---------|
| tests/conftest.py | db_session | session | 15 tests |
| tests/cli/conftest.py | cli_runner | function | 8 tests |

### Issues Found
1. **Duplicate**: `sample_project_path` in test_a.py and test_b.py
   - Action: Move to tests/cli/conftest.py

2. **Missing conftest**: tests/core/workflow/ has no conftest
   - Action: Create with shared fixtures

### Recommendations
- [ ] Create tests/cli/conftest.py with: cli_runner, mock_console
- [ ] Move get_output() to tests/helpers.py
- [ ] Change db_session scope from function to module

Quality Checklist

• No duplicate fixture definitions across files
• Fixtures use narrowest appropriate scope
• conftest.py exists for directories with 3+ test files
• Helper functions in helpers.py, not test files
• Fixtures have docstrings explaining purpose
• Factory pattern used for flexible data creation