Implementing Property Testing with Abstract Classes and Abstract a Fixture with Pytest

You are currently viewing Implementing Property Testing with Abstract Classes and Abstract a Fixture with Pytest
abstract a fixture with `pytest`

Introduction

In object-oriented programming, abstract classes provide a way to define common interfaces and behaviors that can be inherited by multiple subclasses. When working with abstract classes, it is often necessary to test specific properties across all the subclasses. In this article, we will explore an approach to implement property testing using abstract classes in Python, along with the pytest testing framework.

Understanding the Scenario

Let’s start by examining the scenario described in the question. We have an abstract class A, which serves as the base class for multiple subclasses, including B. We want to test a specific property across all the subclasses of A. To achieve this, we will create a test class called APropertyTester, which contains a function for testing the property. Additionally, we will create a test class called TestB that inherits from APropertyTester and specifically tests the property for class B.

Implementing Property Testing

Step 1: Defining the Abstract Class

To begin, we define an abstract class A using the ABC module. This class contains an abstract method called property(), which should be implemented by its subclasses. The property() method will be the property we want to test.

Step 2: Implementing a Subclass

Next, we create a subclass B that inherits from the abstract class A. In this subclass, we implement the property() method and define its behavior. For demonstration purposes, we simply return True as the property value in this example.

Step 3: Creating a Property Tester Class

Now, we create a class called APropertyTester, which will serve as the base class for our property testing. This class contains a method named test_property(), which takes a parameter tested_class. The purpose of this method is to test the property on the provided tested_class instance.

Step 4: Implementing the Property Test Method

Within the test_property() method of the APropertyTester class, we can perform assertions to test the property of the tested_class. In our example, we use the assert statement to validate that the property() method of the tested_class returns True. You can modify this assertion based on your specific property testing requirements.

Step 5: Creating a Test Class

To test the property for a specific subclass, we create a test class that inherits from APropertyTester. In this case, we create a class called TestB to test the property for class B.

Step 6: Implementing a Fixture

In pytest, fixtures are used to provide reusable resources or objects to test functions or classes. In our scenario, we want to provide an instance of class A as a fixture to the TestB class. To achieve this, we define a fixture method within the TestB class and use the @pytest.fixture() decorator. This method returns an instance of class A, which will be used by the test cases in TestB.

Step 7: Running the Tests

Finally, you can run the tests using pytest. Pytest automatically detects the test classes and methods based on its naming conventions. By running pytest in the terminal, pytest will discover and execute the tests defined in the test classes, including the property tests.

import pytest
from abc import ABC, abstractmethod

class A(ABC):
    @abstractmethod
    def property(self):
        raise NotImplementedError

class B(A):
    def property(self):
        return True

class APropertyTester:
    def test_property(self, tested_class):
        assert tested_class.property()

class TestB(APropertyTester):
    @pytest.fixture()
    def tested_class(self):
        return B()

# Run the tests with pytest

pytest

Conclusion

In this article, we explored an approach to implement property testing using abstract classes and the pytest framework in Python. By creating a test class that inherits from a base property tester class, we can define property tests that are automatically executed for each subclass of the abstract class. The use of fixtures allows us to provide the instances of the subclasses as test resources. This methodology provides a structured way to test common properties across multiple subclasses and promotes code reusability and maintainability.