SMTPDFix: Test email, locally

A simple SMTP server based on aiosmtpd for use as a fixture with pytest that supports encryption and authentication. All this does is receives messages and appends them to a list as an email.Message.

This fixture is intended to address use-cases where to test an application that sends an email it needs to be intercepted for subsequent processing. For example, sending an email with a code for password reset or two-factor authentication. This fixture allows a test to trigger the email being sent, ensure that it's sent, and read the code from the email.

Installing

Install using pip:

pip install smtpdfix

Or, if you're using setuptools, it can be included in the tests_require section of a setup.py file:

setup(
    ...
    tests_require = [
        "pytest",
        "smtpdfix",
    ],
)

Using

To use the smtpd add pytest_plugins = "smtpfix" to your code. for example:

# test_mail.py
from smtplib import SMTP

from smtpdfix import smtpd


def test_sendmail(smtpd):
    from_addr = "from.addr@example.org"
    to_addrs = "to.addr@example.org"
    msg = f"From: {from_addr}\r\nTo: {to_addrs}\r\nSubject: Foo\r\n\r\nFoo bar"

    with SMTP(smtpd.hostname, smtpd.port) as client:
        client.sendmail(from_addr, to_addrs, msg)

    assert len(smtpd.messages) == 1

To use STARTTLS:

from smtplib import SMTP

import pytest

pytest_plugins = "smtpdfix"


def test_sendmail(monkeypatch, smtpd):
    monkeypatch.setenv('SMTPD_USE_STARTTLS', 'True')
    from_ = "from.addr@example.org"
    to_ = "to.addr@example.org"
    msg = f"From: {from_}\r\nTo: {to_}\r\nSubject: Foo\r\n\r\nFoo bar"

    with SMTP(smtpd.hostname, smtpd.port) as client:
        client.starttls()  # Note that you need to call starttls first.
        client.sendmail(from_addr, to_addrs, msg)

    assert len(smtpd.messages) == 1

The certificates included with the fixture will work for addresses localhost, localhost.localdomain, 127.0.0.1, 0.0.0.1, ::1. If using other addresses the key (key.pem) and certificate (cert.pem) must be in a location specified under SMTP_SSL_CERTS_PATH.

Configuration

Configuration can be handled through environment variables:

If these variables are included in a .env file they'll be loaded automatically.

Developing

To develop and test smtpdfix you will need to install pytest-asyncio to run asynchronous tests, isort to sort imports and flake8 to lint. To install in a virtual environment for development:

python -m venv venv
./venv/scripts/activate
pip install -e .[dev]

Code is tested using pytest:

pytest

Before submitting a pull request with your changes you should ensure that all imports are sorted and that the code passes linting with flake8.

# Sorting the imports
isort .

# Linting the code
flake8 .

Known Issues

• Firewalls may interfere with the operation of the smtp server.
• Authenticating with LOGIN and PLAIN mechanisms fails over TLS/SSL, but works with STARTTLS. Issue #10
• Currently no support for termination through signals. Issue #4
• Key and certificate for encrypted communications must be called key.pem and cert.pem respectively. Issue #15

©2020-2021, Written with ☕ and ❤ in Montreal, QC