pytest-neon 0.6.0

Pytest plugin for Neon database branch isolation in tests

pytest-neon

Pytest plugin for Neon database branch isolation in tests.

Each test gets its own isolated database state via Neon's instant branching and reset features. Branches are automatically cleaned up after tests complete.

Features

• Isolated test environments: Each test runs against a clean database state
• Fast resets: ~0.5s per test to reset the branch (not create a new one)
• Automatic cleanup: Branches are deleted after tests, with auto-expiry fallback
• Zero infrastructure: No Docker, no local Postgres, no manual setup
• Real database testing: Test against actual Postgres with your production schema
• Automatic DATABASE_URL: Connection string is set in environment automatically
• Driver agnostic: Bring your own driver, or use the optional convenience fixtures

Installation

Core package (bring your own database driver):

pip install pytest-neon

With optional convenience fixtures:

# For psycopg v3 (recommended)
pip install pytest-neon[psycopg]

# For psycopg2 (legacy)
pip install pytest-neon[psycopg2]

# For SQLAlchemy
pip install pytest-neon[sqlalchemy]

# Multiple extras
pip install pytest-neon[psycopg,sqlalchemy]

Quick Start

1. Set environment variables:

export NEON_API_KEY="your-api-key"
export NEON_PROJECT_ID="your-project-id"

2. Write tests:

def test_user_creation(neon_branch):
    # DATABASE_URL is automatically set to the test branch
    import psycopg  # Your own install

    with psycopg.connect() as conn:  # Uses DATABASE_URL by default
        with conn.cursor() as cur:
            cur.execute("INSERT INTO users (email) VALUES ('[e-mail]')")
        conn.commit()

3. Run tests:

pytest

Fixtures

neon_branch (default, recommended)

The primary fixture for database testing. Creates one branch per test session, then resets it to the parent branch's state after each test. This provides test isolation with ~0.5s overhead per test.

Returns a NeonBranch dataclass with:

• branch_id: The Neon branch ID
• project_id: The Neon project ID
• connection_string: Full PostgreSQL connection URI
• host: The database host
• parent_id: The parent branch ID (used for resets)

import os

def test_branch_info(neon_branch):
    # DATABASE_URL is set automatically
    assert os.environ["DATABASE_URL"] == neon_branch.connection_string

    # Use with any driver
    import psycopg
    conn = psycopg.connect(neon_branch.connection_string)

Performance: ~1.5s initial setup per session + ~0.5s reset per test. For 10 tests, expect ~6.5s total overhead.

neon_branch_shared (fastest, no isolation)

Creates one branch per test module and shares it across all tests without resetting. This is the fastest option but tests can see each other's data modifications.

def test_read_only_query(neon_branch_shared):
    # Fast: no reset between tests
    # Warning: data from other tests in this module may be visible
    conn = psycopg.connect(neon_branch_shared.connection_string)

Use this when:

• Tests are read-only
• Tests don't interfere with each other
• You manually clean up test data
• Maximum speed is more important than isolation

Performance: ~1.5s initial setup per module, no per-test overhead.

neon_connection_psycopg (psycopg v3)

Convenience fixture providing a psycopg v3 connection with automatic rollback and cleanup.

Requires: pip install pytest-neon[psycopg]

def test_insert(neon_connection_psycopg):
    with neon_connection_psycopg.cursor() as cur:
        cur.execute("INSERT INTO users (name) VALUES (%s)", ("test",))
    neon_connection_psycopg.commit()

    with neon_connection_psycopg.cursor() as cur:
        cur.execute("SELECT name FROM users")
        assert cur.fetchone()[0] == "test"

neon_connection (psycopg2)

Convenience fixture providing a psycopg2 connection with automatic rollback and cleanup.

Requires: pip install pytest-neon[psycopg2]

def test_insert(neon_connection):
    cur = neon_connection.cursor()
    cur.execute("INSERT INTO users (name) VALUES (%s)", ("test",))
    neon_connection.commit()

neon_engine (SQLAlchemy)

Convenience fixture providing a SQLAlchemy engine with automatic disposal.

Requires: pip install pytest-neon[sqlalchemy]

from sqlalchemy import text

def test_query(neon_engine):
    with neon_engine.connect() as conn:
        result = conn.execute(text("SELECT 1"))
        assert result.scalar() == 1

Using Your Own SQLAlchemy Engine

If you have a module-level SQLAlchemy engine (common pattern), you must use pool_pre_ping=True:

# database.py
from sqlalchemy import create_engine
from config import DATABASE_URL

# pool_pre_ping=True is REQUIRED for pytest-neon
# It verifies connections are alive before using them
engine = create_engine(DATABASE_URL, pool_pre_ping=True)

Why? After each test, pytest-neon resets the branch which terminates server-side connections. Without pool_pre_ping, SQLAlchemy may try to reuse a dead pooled connection, causing SSL connection has been closed unexpectedly errors.

This is also a best practice for any cloud database (Neon, RDS, etc.) where connections can be terminated externally.

Migrations

pytest-neon supports running migrations once before tests, with all test resets preserving the migrated state.

Smart Migration Detection

The plugin automatically detects whether migrations actually modified the database schema. This optimization:

• Saves Neon costs: No extra branch created when migrations don't change anything
• Saves branch slots: Neon projects have branch limits; this avoids wasting them
• Zero configuration: Works automatically with any migration tool

When a second branch is created:

• Only when neon_apply_migrations is overridden AND the schema actually changes

When only one branch is used:

• If you don't override neon_apply_migrations (no migrations defined)
• If your migrations are already applied (schema unchanged)

The detection works by comparing a fingerprint of information_schema.columns before and after migrations run.

How It Works

When migrations actually modify the schema, the plugin uses a two-branch architecture:

Parent Branch (your configured parent)
    └── Migration Branch (session-scoped)
            │   ↑ migrations run here ONCE
            └── Test Branch (session-scoped)
                    ↑ resets to migration branch after each test

When no schema changes occur, the plugin uses a single-branch architecture:

Parent Branch (your configured parent)
    └── Migration/Test Branch (session-scoped)
            ↑ resets to parent after each test

This means:

• Migrations run once per test session (not per test or per module)
• Each test reset restores to the post-migration state
• Tests always see your migrated schema

Setup

Override the neon_apply_migrations fixture in your conftest.py:

Alembic:

# conftest.py
import subprocess
import pytest

@pytest.fixture(scope="session")
def neon_apply_migrations(_neon_migration_branch):
    """Run Alembic migrations before tests."""
    # DATABASE_URL is already set to the migration branch
    subprocess.run(["alembic", "upgrade", "head"], check=True)

Django:

# conftest.py
import pytest

@pytest.fixture(scope="session")
def neon_apply_migrations(_neon_migration_branch):
    """Run Django migrations before tests."""
    from django.core.management import call_command
    call_command("migrate", "--noinput")

Raw SQL:

# conftest.py
import pytest

@pytest.fixture(scope="session")
def neon_apply_migrations(_neon_migration_branch):
    """Apply schema from SQL file."""
    import psycopg
    with psycopg.connect(_neon_migration_branch.connection_string) as conn:
        with open("schema.sql") as f:
            conn.execute(f.read())
        conn.commit()

Custom migration tool:

# conftest.py
import pytest

@pytest.fixture(scope="session")
def neon_apply_migrations(_neon_migration_branch):
    """Run custom migrations."""
    from myapp.migrations import run_migrations
    run_migrations(_neon_migration_branch.connection_string)

Important Notes

• The _neon_migration_branch parameter gives you access to the NeonBranch object with connection_string, branch_id, etc.
• DATABASE_URL (or your configured env var) is automatically set when the fixture runs
• If you don't override neon_apply_migrations, no migrations run (the fixture is a no-op by default)
• Migrations run before any test branches are created, so all tests see the same migrated schema

Configuration

Environment Variables

Variable	Description	Required
NEON_API_KEY	Your Neon API key	Yes
NEON_PROJECT_ID	Your Neon project ID	Yes
NEON_PARENT_BRANCH_ID	Parent branch to create test branches from	No
NEON_DATABASE	Database name (default: neondb)	No
NEON_ROLE	Database role (default: neondb_owner)	No

Command Line Options

Option	Description	Default
--neon-api-key	Neon API key	NEON_API_KEY env
--neon-project-id	Neon project ID	NEON_PROJECT_ID env
--neon-parent-branch	Parent branch ID	Project default
--neon-database	Database name	neondb
--neon-role	Database role	neondb_owner
--neon-keep-branches	Don't delete branches after tests	false
--neon-branch-expiry	Branch auto-expiry in seconds	600 (10 min)
--neon-env-var	Environment variable for connection string	DATABASE_URL

Examples:

# Keep branches for debugging
pytest --neon-keep-branches

# Disable auto-expiry
pytest --neon-branch-expiry=0

# Use a different env var
pytest --neon-env-var=TEST_DATABASE_URL

pyproject.toml / pytest.ini

You can also configure options in your pyproject.toml:

[tool.pytest.ini_options]
neon_database = "mydb"
neon_role = "myrole"
neon_keep_branches = true
neon_branch_expiry = "300"

Or in pytest.ini:

[pytest]
neon_database = mydb
neon_role = myrole
neon_keep_branches = true
neon_branch_expiry = 300

Priority order: CLI options > environment variables > ini settings > defaults

CI/CD Integration

GitHub Actions

name: Tests

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
        with:
          python-version: '3.12'

      - name: Install dependencies
        run: pip install -e .[psycopg,dev]

      - name: Run tests
        env:
          NEON_API_KEY: ${{ secrets.NEON_API_KEY }}
          NEON_PROJECT_ID: ${{ secrets.NEON_PROJECT_ID }}
        run: pytest

How It Works

1. At the start of the test session, the plugin creates a new Neon branch from your parent branch
2. DATABASE_URL is set to point to the new branch
3. Tests run against this isolated branch with full access to your schema and data
4. After each test, the branch is reset to its parent state (~0.5s)
5. After all tests complete, the branch is deleted
6. As a safety net, branches auto-expire after 10 minutes even if cleanup fails

Branches use copy-on-write storage, so you only pay for data that differs from the parent branch.

What Reset Does

The neon_branch fixture uses Neon's branch restore API to reset database state after each test:

• Data changes are reverted: All INSERT, UPDATE, DELETE operations are undone
• Schema changes are reverted: CREATE TABLE, ALTER TABLE, DROP TABLE, etc. are undone
• Sequences are reset: Auto-increment counters return to parent state
• Complete rollback: The branch is restored to the exact state of the parent at the time the child branch was created

This is similar to database transactions but at the branch level.

Limitations

Parallel Test Execution

This plugin sets the DATABASE_URL environment variable, which is process-global. This means it is not compatible with pytest-xdist or other parallel test runners that run tests in the same process.

If you need parallel execution, you can:

• Use neon_branch.connection_string directly instead of relying on DATABASE_URL
• Run with pytest-xdist --dist=loadfile to keep modules in separate processes
• Run tests serially (default pytest behavior)

Troubleshooting

"psycopg not installed" or "psycopg2 not installed"

The convenience fixtures require their respective drivers. Install the appropriate extra:

# For neon_connection_psycopg fixture
pip install pytest-neon[psycopg]

# For neon_connection fixture
pip install pytest-neon[psycopg2]

# For neon_engine fixture
pip install pytest-neon[sqlalchemy]

Or use the core neon_branch fixture with your own driver:

def test_example(neon_branch):
    import my_preferred_driver
    conn = my_preferred_driver.connect(neon_branch.connection_string)

"Neon API key not configured"

Set the NEON_API_KEY environment variable or use the --neon-api-key CLI option.

"Neon project ID not configured"

Set the NEON_PROJECT_ID environment variable or use the --neon-project-id CLI option.

"SSL connection has been closed unexpectedly" (SQLAlchemy)

This happens when SQLAlchemy tries to reuse a pooled connection after a branch reset. The reset terminates server-side connections, but SQLAlchemy's pool doesn't know.

Fix: Add pool_pre_ping=True to your engine:

engine = create_engine(DATABASE_URL, pool_pre_ping=True)

This makes SQLAlchemy verify connections before using them, automatically discarding stale ones.

License

MIT