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 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 email.
Installing
To install using pip, first upgrade pip to the latest version to avoid any issues installing cryptography:
$ python -m pip install --upgrade pip
$ pip install smtpdfix
Or, if you're using setuptools, it can be included in the extras_require argument of a setup.py file:
setup(
...
extras_require={
"test": [
"pytest",
"smtpdfix",
],
},
)
and then installed with pip (-e assumes that you want your project to be editable):
$ python -m pip install --upgrade pip
$ pip install -e .[test]
Using
The SMTPDFix plugin, smtpd, automatically registers for use with pytest when you install smtpdfix. To use it simply add to you test method.
from smtplib import SMTP
def test_sendmail(smtpd):
from_addr = "[email protected]"
to_addrs = "[email protected]"
msg = (f"From: {from_addr}\r\n"
f"To: {to_addrs}\r\n"
f"Subject: Foo\r\n\r\n"
f"Foo 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
def test_sendmail(smtpd):
smptd.config.use_starttls = True
from_ = "[email protected]"
to_ = "[email protected]"
msg = (f"From: {from_}\r\n"
f"To: {to_}\r\n"
f"Subject: Foo\r\n\r\n"
f"Foo 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
As of version 0.2.7 the plugin automatically registers and it is not necessary to include it manually by adding
pytest_plugins = "smtpdfix"to the module or conftest.py.
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.
Not as a fixture
In some situations it may be desirable to not use the fixture which is initialized before entering the test. This can be accomplished by using the SMTPDFix class.
from smtplib import SMTP
from smtpdfix import SMTPDFix
def test_smtpdfix(msg):
hostname, port = "127.0.0.1", 8025
with SMTPDFix(hostname, port) as smtpd:
with SMTP(hostname, port) as client:
from_addr = "[email protected]"
to_addrs = "[email protected]"
msg = (f"From: {from_addr}\r\n"
f"To: {to_addrs}\r\n"
f"Subject: Foo\r\n\r\n"
f"Foo bar")
client.sendmail(from_addr, to_addrs, msg)
assert len(smtpd.messages) == 1
Configuration
Configuration is handled through properties in the config of the fixture and are initially set from environment variables:
| Property | Variable | Default | Description |
|---|---|---|---|
host |
SMTPD_HOST |
127.0.0.1 or ::1 |
The hostname that the fixture will listen on. |
port |
SMTPD_PORT |
8025 |
The port that the fixture will listen on. |
ready_timeout |
SMTPD_READY_TIMEOUT |
5.0 |
The seconds the server will wait to start before raising a TimeoutError. |
login_username |
SMTPD_LOGIN_NAME |
user |
|
login_password |
SMTPD_LOGIN_PASSWORD |
password |
|
use_ssl |
SMTPD_USE_SSL |
False |
Whether the fixture should use fixed TLS/SSL for transactions. If using smtplib requires that SMTP_SSL be used instead of SMTP. |
use_starttls |
SMTPD_USE_STARTTLS |
False |
Whether the fixture should use StartTLS to encrypt the connections. If using smtplib requires that SMTP.starttls() is called before other commands are issued. Overrides use_tls as the preferred method for securing communications with the client. |
enforce_auth |
SMTPD_ENFORCE_AUTH |
False |
If set to true then the fixture refuses MAIL, RCPT, DATA commands until authentication is completed. |
ssl_cert_path |
SMTPD_SSL_CERTS_PATH |
./certs/ |
The path to the key and certificate in PEM format for encryption with SSL/TLS or StartTLS. |
ssl_cert_files |
SMTPD_SSL_CERT_FILE and SMTPD_SSL_KEY_FILE |
("cert.pem", None) |
A tuple of the path for the certificate file and key file in PEM format. See Resolving certificate and key paths for more details. |
If environment variables are included in a
.envfile they'll be loaded automatically.
Resolving certificate and key paths
In order to resolve the certificate and key paths for the SSL/TLS context SMTPDFix does the following:
- On initialization of a
smtpdfix.Configthessl_cert_pathis set by theSMTPD_SSL_CERTS_PATHenvironment variable and thessl_cert_filesis set to a tuple of(SMTPD_SSL_CERT_FILE and SMTPD_SSL_KEY_FILE). If the environment variables are not set the deafults are used. - If an SSL Context is needed, when the
smptdfix.AuthControlleris initialized it will attempt to find the files in the following sequence for both the certificate file and the key file:- If the value in
ssl_cert_filesisNonethenNoneis returned. Setting the key file to be none assumes that it has been included in the certificate file. - If the value in
ssl_cert_filesis a valid path to a file then this is returned. ssl_cert_pathand the value fromssl_cert_filesare joined and returned if it a valid path to a file.- A
FileNotFoundErroris raised.
- If the value in
An example, assuming that the certificate and key are written in a single PEM file located at ./certificates/localhost.cert.pem would be:
from smtplib import STMP_SSL
def test_custom_certificate(smtpd):
smtpd.config.ssl_cert_files = "./certificates/localhost.cert.pem"
smtpd.config.use_ssl = True
from_ = "[email protected]"
to_ = "[email protected]"
msg = (f"From: {from_}\r\n"
f"To: {to_}\r\n"
f"Subject: Foo\r\n\r\n"
f"Foo bar")
with SMTP_SSL(smtpd.hostname, smtpd.port) as client:
client.sendmail(from_addr, to_addrs, msg)
assert len(smtpd.messages) == 1
Alternatives
Many libraries for sending email have built-in methods for testing and using these methods should generally be prefered over SMTPDFix. Some known solutions:
- fastapi-mail: has a
record_messsages()method to intercept the mail. Instructions on how to suppress the sending of mail and implement it can be seen at https://sabuhish.github.io/fastapi-mail/example/#unittests-using-fastapimail - flask-mail: has a method to suppress sending and capture the email for testing purposes. Instructions
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 tox:
$ tox
Quick tests can be handled by running pytest directly:
$ pytest -p no:smtpd --cov
Before submitting a pull request with your changes you should ensure that all imports are sorted and that the code passes linting with flake8.
$ isort .
$ flake8 .
If you have upgraded or added any requirements you should add them to setup.py along with the minimal constraints needed for the functionality. The requirements.txt file can then be updated by running:
$ bash ./scripts/fix-requirements.sh .
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
- If the fixture start exceeds the
ready_timeoutand aborts the host and port are not consistently released and subsequent uses may result in an error. Issue #80
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