Introduction to pytest
Software testing is an important process in the development lifecycle of software. It enables developers to detect bugs and regressions before releasing software to the public.
It helps in boosting the confidence of the developers, which can be achieved through thorough testing. There are several tools available for software testing, but pytest stands out as a feature-rich and powerful testing tool.
In this article, we will explore the benefits of using pytest, its features, and how it compares to unittest.
Benefits of pytest
Testing productivity: One of the primary benefits of pytest is its testing productivity. This is achieved by reducing the amount of boilerplate code required for testing.
With pytest, developers can write less code to test the same functionality. This is due to the fact that pytest is designed to work with Python’s assert keyword, which is simpler and more expressive than unittest’s assertion functions.
Confidence: Pytest boosts the confidence of developers by providing a comprehensive testing framework. With pytest, developers can write tests that cover all possible test cases, enabling them to detect regressions early on.
This helps in avoiding bugs and ensuring that the software works as intended. Regressions: Pytest makes it easy to detect regressions.
When a regression occurs, pytest will output an error message that indicates the source of the problem. This makes it easy to quickly identify and fix the issue.
Tools: Pytest has a plugin-based ecosystem that makes it easy to integrate with other tools. This means that developers can extend the functionality of pytest by installing plugins that automate tasks such as test discovery, test parallelization, and coverage reporting.
Boost: Pytest is a powerful and flexible testing tool that can be customized to meet the needs of any project. With pytest, developers can write tests that are easy to read, maintain, and understand, saving time and helping to improve productivity.
Shortcomings of unittest
Despite its popularity, unittest has some limitations and issues that make it less desirable for modern software development. One of the main shortcomings of unittest is the amount of boilerplate code that is required to write tests.
This can lead to code duplication and make it difficult to read, maintain, and understand. Another issue with unittest is that it is not very flexible.
It is designed to work with Python’s built-in assertion functions, which can be limiting. This means that developers may have to write more code to achieve the same functionality as with pytest.
Finally, unittest is not very extensible. It lacks a powerful plugin system, which means that developers cannot easily extend the functionality of unittest by installing plugins.
Features of pytest
One of the standout features of pytest is its simplicity. Pytest uses an Arrange-Act-Assert (AAA) model for organizing tests, which makes it easy to understand and read.
With this model, developers can clearly delineate the setup, execution, and verification phases of testing, making it easy to write, maintain, and understand test code. Pytest also reduces the amount of boilerplate code required for testing.
This is achieved by using Python’s assert keyword, which is more expressive and simpler than unittest’s assertion functions. This means that developers can write tests that are shorter and more readable, saving time and improving productivity.
Pytest is also flexible and extensible. It has a plugin-based ecosystem that makes it easy to install and use plugins that extend its functionality.
This means that developers can easily customize pytest to meet the needs of their projects. Pytest is also backward compatible with unittest.
This means that developers can easily switch from unittest
to pytest without having to rewrite their existing test suites.
Conclusion
In conclusion, pytest is a feature-rich and powerful testing tool that can help developers improve their testing productivity, boost their confidence, and detect regressions early on. It also has a plugin-based ecosystem that makes it easy to extend its functionality and customize it for specific project needs.
Compared to unittest, pytest is simpler, more flexible, and requires less boilerplate code, which can save time and improve productivity. With these benefits, it’s no wonder that pytest has become one of the most popular testing tools in use today.
Nicer Output
Pytest is not only a powerful testing tool, but it also provides a nicer output compared to other testing tools. Pytest’s output is designed to be easy to read, informative, and helpful when troubleshooting issues.
Pytest Command Usage
To use pytest, developers can simply run the “pytest” command. This will start the test session, which will automatically discover and run all the tests in the current directory and its subdirectories.
Developers can also specify additional options to customize the test session, such as platform or versions of Python.
The rootdir option can also be used to specify the root directory for test discovery.
This can be useful when testing modules that are not in the same directory as the test module.
Progress and Status Display
During test execution, pytest displays a progress and status display for each test. This display shows tests that are passing with a dot (“.”), failing tests with an “F” and errors with an “E”.
This makes it easy for developers to quickly see which tests have passed and which ones are failing. At the end of the test session, pytest provides a summary of the test results.
This summary includes the number of tests that succeeded, failed, and were skipped. This helps developers to quickly identify any potential issues with their code and decide whether to ship the code.
Detailed Failure Reporting
When a test fails, pytest provides a detailed failure report. This report includes the assertion that failed and a traceback that shows the exact line of code that caused the failure.
This makes it easy for developers to identify the source of the problem and fix it quickly. Pytest also provides detailed failure reports for all tests, even for the ones that were not expecting any failures.
This helps developers to easily identify test cases that are passing when they should not be.
Less to Learn
Another benefit of using pytest is that it requires less to learn than other testing frameworks. Pytest uses the assert keyword for writing assertions, which is already familiar to most programmers.
This means that developers do not need to learn new assertion functions to write tests in pytest. Pytest also encourages small, self-contained tests.
This means that each test should be isolated from other tests and should only test one thing at a time. This helps to ensure that the test results are accurate and that issues can be easily identified and fixed.
By using pytest, developers can improve their testing process and achieve more confidence in their code. With its simpler syntax, flexible plugin-based ecosystem, powerful reporting tools and an improved output, Pytest is a developer-friendly, efficient, and productive testing framework.
Easier to Manage State and Dependencies
One area where pytest stands out compared to unittest is in the management of state and dependencies in tests. Pytest makes it easier to manage dependencies and state, which can save time and improve productivity.
Implicit Dependencies in Unittest
In unittest, dependencies are often implicit. This means that setting up the test environment requires the use of setUp() and tearDown() methods.
These methods can be complex and error-prone when handling different types of dependencies. It also means that changing the dependencies requires changing both the setUp() and the test method, which can be time-consuming.
For example, consider a test that requires a database connection. In setUp(), the connection must be established, and in tearDown(), it must be closed.
This added complexity makes it difficult to manage the state and dependencies in a test.
Explicit Dependencies with Pytest Fixtures
With pytest, explicit dependencies can be defined using fixtures. Fixtures are functions that provide data or other resources to tests.
These functions can be explicitly defined and reused across different tests. This makes it easier to manage dependencies and state, and reduces the amount of boilerplate code needed for testing.
For example, a fixture can be created to establish a database connection and provide that connection to any test that requires it. This means that changing the database connection only requires a change in the fixture, rather than both the fixture and the test method.
Fixture functions can also be defined with parameters, making them even more flexible. This enables developers to provide different resources and data to different tests or to reuse fixtures for different contexts.
Easy to Filter Tests
Another area where pytest shines is in filtering tests. Pytest provides multiple ways to filter tests such as by test name, directory or categorization.
Name-Based Filtering
Pytest has a -k parameter, which can be used to filter tests by their names. Developers can specify a search term, and pytest will run only tests that have that term in their fully qualified names.
This can be useful when a test suite contains many tests, and developers want to focus on specific ones. For example, if a test suite contains several tests that deal with login functionality, developers can specify “login” as the search term.
Pytest will then run only the tests that have “login” in their names.
Directory Scoping
Pytest provides an easy way to scope test runs to the current directory. Developers can use the -x parameter to tell pytest to stop running the test session after the first failure it encounters.
This can save time when tests fail early in the test session.
Test Categorization
Pytest also provides a way to categorize tests using marks. Marks can be used to group tests together by category.
This enables developers to run specific sets of tests and exclude others during a test run. For example, if a test suite contains tests that require the network connection, developers can use a “@pytest.mark.network” mark to group the tests together.
Then, developers can use the “-m” parameter to run only tests with that mark.
Conclusion
Overall, Pytest is a powerful and flexible testing tool that can help developers to manage state and dependencies in their tests more easily. Its use of explicit dependencies with fixtures makes it simpler and less error-prone than unittest’s implicit dependencies.
Also, its filtering capabilities make it easy to run specific tests, saving time and improving productivity. By adopting Pytest, developers can streamline their testing process and increase their confidence in their code.
Allows Test Parametrization
One of the standout features of pytest is its ability to allow test parametrization. This feature allows developers to run the same test code with multiple inputs, making it possible to test multiple scenarios in one run.
Duplicating Test Code in Unittest
In unittest, if there are similar tests that need to be run with different input values, developers must duplicate the test code for each input value. This can lead to a lot of code duplication and make the code difficult to read, manage and maintain.
Parametrization with Pytest
However, with pytest, developers can use parametrized tests to avoid duplicating the same sets of tests with different input values. Parametrized tests allow developers to run the same test code with multiple input values, which adds to the modularity of the test.
To create a parameterized test in Pytest, developers create a single test function and add multiple input-output tuples as arguments using @pytest.mark.parametrize decorator. Pytest will then run the test function multiple times, once for each set of input values provided.
Using this approach significantly reduces code duplication while providing independent test results for each input scenario.
Has a Plugin-Based Architecture
Pytest’s plugin-based architecture allows developers to customize the tool to meet their project-specific needs, which can save time and improve productivity.
Customization with Pytest Plugins
Pytest plugins add extra functionality to the base pytest, allowing developers to extend its capabilities and customize pytest to suit their specific needs. Plugins can be used for test discovery, test execution, reporting, and other purposes.
This makes it easy to integrate pytest with other tools and frameworks.
Specific and General Pytest Plugins
There are many specific and general pytest plugins available. Some of the most popular plugins include:
- pytest-django: This plugin offers various fixtures and other functionality that make it easier to test Django applications.
- pytest-cov: This plugin generates coverage reports during test runs, providing metrics on code coverage. – pytest-instafail: This plugin immediately stops a test run at the first failure, which can save time during debugging.
Other plugins are designed for specific use cases such as testing REST APIs, testing emails, testing Selenium-based applications. Thus, this creates an environment where developers can choose the plugins that are specific to their project needs and not waste time using unwanted plugins.
In addition to these specific plugins, there are also many general plugins available that provide a wide range of features, from improving test output to simplifying test discovery and execution.
Conclusion
Pytest is a powerful testing framework that can save developers time and effort by providing better test discovery, allowing for customizable fixtures, detailed reporting, test categorization, test filtering, and many other useful features. The ability to parametrize tests and not creating duplicate tests allows developers to write lean and modular code.
Meanwhile, its plugin-based architecture and broad ecosystem of plugins make it easy to customize pytest to suit project-specific needs. Overall, Pytest is an excellent tool for modern software development and should be an essential tool in any developer’s toolkit.
Fixtures: Managing State and Dependencies (continued)
Pytest’s fixtures provide a powerful way to manage state and dependencies in tests. In this section, we will explore a practical example of how fixtures can be used in software development.
When to Create Fixtures
In Test Driven Development (TDD), fixtures can be created before the code that will use them. This helps to ensure that the code conforms to the requirements that the test has set.
Consider the example of a function named format_data_for_display. Its requirement is to receive a list of people and return a string representing the data of each person.
A test can be created before developing the function. The test will expect a specific format that the function must return.
Writing a Test for format_data_for_display
def test_format_data_for_display():
people = [
{"name": "Alice", "age": 25},
{"name": "Bob", "age": 30},
]
result = format_data_for_display(people)
expected_result = "Alice, 25nBob, 30n"
assert result == expected_result
Fixture Providing Data for the Test
The people list defined in the test above can be easily considered a fixture. It provides the data that the test needs to work.
Instead of creating it inside each test function, it can be extracted into a fixture function. Lets look at the fixture code for people.
@pytest.fixture
def people():
return [
{"name": "Alice", "age": 25},
{"name": "Bob", "age": 30},
]
Now, the test code can be simplified as follows, using the `people` fixture.
def test_format_data_for_display(people):
result = format_data_for_display(people)
expected_result = "Alice, 25nBob, 30n"
assert result == expected_result
Here, the `people` fixture is provided as an argument to the test function and can be incorrectly used in the test.
This example shows how fixtures can help to simplify test code and promote code reusability. Fixtures iteratively can also be customized with parameters to allow for explicit dependencies.
This helps developers to manage dependencies and state, and reduces the amount of boilerplate code required for tests.
In conclusion, fixtures can make tests more straightforward to write, more manageable, and more readable.
As fixtures remove a lot of code duplication, developers using Pytest can write cleaner code and debugging can be much easier.