fakesnow ❄️

Fake Snowflake Connector for Python. Run and mock Snowflake DB locally.

Install

pip install fakesnow

Usage

Run script.py with fakesnow:

fakesnow script.py

Or a module, eg: pytest

fakesnow -m pytest

fakesnow executes fakesnow.patch before running the script or module.

fakesnow.patch

To use fakesnow within your code:

import fakesnow
import snowflake.connector

with fakesnow.patch():
    conn = snowflake.connector.connect()

    print(conn.cursor().execute("SELECT 'Hello fake world!'").fetchone())

The following imports are automatically patched:

• import snowflake.connector.connect
• import snowflake.connector.pandas_tools.write_pandas

To patch modules that use the from ... import syntax, manually specify them, eg: if mymodule.py has the import:

from snowflake.connector.pandas_tools import write_pandas

Then patch it using:

with fakesnow.patch("mymodule.write_pandas"):
    ...

By default databases are in-memory. To persist databases between processes, specify a databases path:

with fakesnow.patch(db_path="databases/"):
    ...

pytest fixtures

pytest fixtures are provided for testing. Example conftest.py:

from typing import Iterator

import fakesnow.fixtures
import pytest

pytest_plugins = fakesnow.fixtures.__name__

@pytest.fixture(scope="session", autouse=True)
def setup(_fakesnow_session: None) -> Iterator[None]:
    # the standard imports are now patched
    ...
    yield

Or with from ... import patch targets:

from typing import Iterator

import fakesnow
import pytest

@pytest.fixture(scope="session", autouse=True)
def _fakesnow_session() -> Iterator[None]:
    with fakesnow.patch("mymodule.write_pandas"):
        yield

Implementation coverage

• cursors and standard SQL
• get_result_batches()
• information schema
• multiple databases
• parameter binding
• table comments
• write_pandas(..)
• access control
• standalone/out of process api/support for faking non-python connectors
• stored procedures

Partial support

• date functions
• regex functions
• semi-structured data
• tags

For more detail see tests/test_fakes.py

Caveats

• The order of rows is non deterministic and may not match Snowflake unless ORDER BY is fully specified.
• VARCHAR field sizes are not enforced. Unlike Snowflake which errors with "User character length limit (xxx) exceeded by string" when an inserted string exceeds the column limit.

Contributing

See CONTRIBUTING.md to get started and develop in this repo.