Mongoengine is a popular Object-Document Mapping (ODM) library for working with MongoDB in Python. It provides a simple and expressive API for interacting with MongoDB, making it easy to manipulate and query data.

In this blog post, we will focus on unit testing with mongoengine. Unit testing is crucial for ensuring the correctness and reliability of your code. It allows you to validate the behavior of individual units or components of your application, such as functions, classes, or modules. Performing unit tests for mongoengine models and queries is important to catch any potential bugs or issues early in the development cycle.

Setting up the environment

Before we dive into writing unit tests, let’s set up our development environment. Start by installing mongoengine using pip:

pip install mongoengine

Next, we’ll need to import mongoengine into our test files:

import mongoengine

Writing unit tests for mongoengine models

When writing unit tests for mongoengine models, we want to ensure that the models are created correctly and that their fields have the expected properties. Let’s take a look at an example:

import unittest
from mongoengine import Document, StringField

class User(Document):
    name = StringField(required=True, max_length=50)
    email = StringField(required=True, unique=True)

class TestUserModel(unittest.TestCase):
    def test_user_model_creation(self):
        user = User(name="John Doe", email="john@example.com")
        self.assertEqual(user.name, "John Doe")
        self.assertEqual(user.email, "john@example.com")

    def test_user_model_fields(self):
        fields = User._fields.keys()
        self.assertIn("name", fields)
        self.assertIn("email", fields)
        self.assertEqual(User._fields["name"].required, True)
        self.assertEqual(User._fields["name"].max_length, 50)
        self.assertEqual(User._fields["email"].required, True)
        self.assertEqual(User._fields["email"].unique, True)

In the TestUserModel class, we define two test methods: test_user_model_creation and test_user_model_fields.

The test_user_model_creation method creates an instance of the User model with sample data and asserts that the model’s attributes have the expected values.

The test_user_model_fields method checks the existence and properties of the fields defined in the User model. It uses the _fields attribute of the model to access field metadata, such as required and unique properties, and asserts the expected values.

Writing unit tests for mongoengine queries

Another important aspect of testing with mongoengine is validating the correctness of your queries. We can write unit tests to ensure that our queries return the expected results. Let’s illustrate this with an example:

import unittest
from mongoengine import connect, Document, StringField

connect("my_database")

class User(Document):
    name = StringField()

class TestUserQueries(unittest.TestCase):
    @classmethod
    def setUpClass(cls):
        # Create some sample data for testing queries
        User(name="John Doe").save()
        User(name="Jane Smith").save()

    def test_query_users(self):
        users = User.objects(name="John Doe")
        self.assertEqual(len(users), 1)
        self.assertEqual(users.first().name, "John Doe")

    def test_query_nonexistent_user(self):
        users = User.objects(name="Alice")
        self.assertEqual(len(users), 0)

In the example above, we define the TestUserQueries class with two test methods: test_query_users and test_query_nonexistent_user.

The test_query_users method queries the User collection for users with the name “John Doe”. It asserts that the query returns only one result and that the name of the first user is indeed “John Doe”.

The test_query_nonexistent_user method queries the User collection for users with the name “Alice”. Since there are no users with that name, it asserts that the query returns zero results.

Running the unit tests

To run the unit tests, we can use a test runner like unittest built-in to Python. Here’s an example command to run the tests:

python -m unittest test_file.py

Replace test_file.py with the actual filename of your test file.

Writing comprehensive unit tests for mongoengine models and queries ensures the stability and correctness of your codebase. It allows you to confidently make changes and refactor your code without worrying about introducing regressions. So, make sure to incorporate unit testing practices into your development workflow when working with mongoengine in Python.