How to unit test in python (2023)

Confidence in product quality, reliability and dependability are some of the most valuable attributes sought by both consumers and businesses. This trust is built through rigorous product testing.

In software engineering, practices such as extreme development (XP) and test-driven development (TDD) promote the belief that automated testing should be adopted from the very beginning of a project. This means writing tests before building features to instill a high degree of confidence in the product from the start.

Using this approach ensures that every piece of functionality will serve its purpose. An additional advantage is that the functionality meets the requirements and acceptance criteria defined in the project from the very beginning.

Unit testing is the fastest and most common form of automated testing available for software projects.

How to unit test in python (1)

Formation of the basetest piramideUnit tests check small, individual units of functionality in isolation. This also means they are the fastest tests to run, running hundreds of tests per second. This high speed of execution is the reason why there are most of them.

In this article, we'll show you how to get started with unit testing in Python.

(Video) Unit Tests in Python || Python Tutorial || Learn Python Programming

Writing a unit test

In this tutorial, we will build a basic method calledmy_amountwhich requires several variables (we call themAandB) then inside the function each variable is added before returning. For example, if we pass 5 and 10 as inputs, we return 15. Only numbers are accepted as valid inputs, so we add error handling for any input that doesn't meet this requirement.
The first thing we need to do is create a file In it, we will start by downloading the python packageunituse the line. It gives us accessTest casekeyword we need to build our tests.

importing unit tests

Now that we have this, we can do our first test. First we check the output type of our function.

from my_sum import my_sumclass TestingMySum(unittest.TestCase): def test_my_sum_returns_correct_int(self): response = my_sum(5, 10) self.assertTrue(type(respons) is int)

Now we have our first unit test!

The first line of the function calls ourmy_amountfunction, passing 5 and 10 as inputs. The last line above is known as the test statement. A test estimate is a condition we expect the functionality we're testing to meet. They often relate directly or indirectly to the acceptance criteria or requirements you encounter. This connection between assertions and acceptance criteria is why it is so important to use valid assertions to ensure that the software actually does what it is expected to do.

Right now this unit test is checking the response we get from ourmy_amountfunction is an integer (also called an integer). If so, the test is successful. If not, it will fail and display an error so we can find out why it's failing.

If we were to run this test now, an error would occur. That's because it doesn't existmy_amountavailable function. So let's add one.

(Video) Python Tutorial: Unit Testing Your Code with the unittest Module

def mysum(a, b): Vrati a + b

The code above ensures that our test passes. However, there are many scenarios that we are not currently reviewing, so we will add a few additional explanations.

First, let's add a check right after our type check that a valid value is returned. In our existing test, the correct value is 15.

self.assertEqual(odgovor, 15)

The above statement compares our response to a constant value. Additionally, we want to add more tests to see if our functionality works with floating point and negative numbers.

def test_my_sum_returns_correct_float(self): odgovor = my_sum(5, 10.5) self.assertIsNotNone(respons) self.assertTrue(type(respons) is float) self.assertEqual(respons, 15.5)def test_my_sum_returns_correct_with_negatives(self): response = my_sum(- 5, -10) self.assertIsNotNone(odpowiedź) self.assertTrue(typ(odpowiedź) to int) self.assertEqual(odpowiedź, -15)

We also want to make sure that our function returns an error when it returns bad input. This bad input can be letters or objects. To do this, we create some new tests and use the methodconquersone statement that has a slightly different structure than the others.

def test_my_sum_raises_exception_when_passed_strings(self): self.assertRaises(TypeError, my_sum, "halo", "wereld")def test_my_sum_raises_exception_when_passed_lists(self): self.assertRaises(TypeError, my_sum, [6, 7], [1, 2])

Finally, in order for these new tests to succeed, we need to add error handling as part of our functionality. This can be done by modifying our existing code to use itis an examplemethod to check input types and then raiseTypoif type is not integer or float.

def my_sum(a, b): if isinstance(a, (int, float, complex)): if isinstance(b, (int, float, complex)): return a + b raise TypeError

Running a unit test

Next, we'll look at running our tests. However, before we actually run our test, let's add an entry point by adding the following two lines to the end of ourstest_mijn_som.pyduration.

(Video) How To Write Unit Tests For Existing Python Code // Part 1 of 2

if __name__ == '__main__': unittest.main()

Using the command line, we go to the directory that contains our files. Once we are in the same directory, we can run our tests using the python

How to unit test in python (2)

This instructs the command line to use python for executiontest_my_sumfile where it goes to our access point and then gets a command to useunittest runner. A similar way to run this test file from the command line is to use python-m unit_test test_my_sumcommand as shown in the image below.

How to unit test in python (3)

As shown in these screenshots, some text is returned to the command line with information about the test results. The first row shows which tests have failed or failed, using a period (.) to indicate successful tests and an E or F to indicate which have errors or failed. We also get a heap trace for each failed test that explains why each test failed.

Run unit tests in the IDE

These unit tests can also be run from your favorite integrated development environments (IDEs) such as PyCharm or Visual Studio. This makes it more convenient when working with large projects that contain many files.

Perform unit testing in Visual Studio Code

To run tests in Visual Studio Code, you must configure Visual Studio Code to work with your test environment. To do this, let's open the fileTesttab in the sidebar menu.

How to unit test in python (4)

A menu similar to the one above should appear. Press the marked buttonStel python tests in. A drop-down menu appears at the top of the screen. Select from hereunit.

(Video) Unit Testing in Python using unittest framework - Basic Introduction and How to Write Tests

How to unit test in python (5)
How to unit test in python (6)

Then click on the option labeled Test Directory. In this tutorial, this is the root folder with a dot (as shown above). The next set of options asks what sample names we used for our test files. For this guide, it's the option we've chosentest_*.py.

How to unit test in python (7)

Our test program should now be set up correctly, meaning our tests will appear in the fileTestmenu on the left. From here, tests can be run by clicking a buttonRun testsbutton.

How to unit test in python (8)

Each successful test is marked with a green tick, and each unsuccessful test is marked with a red cross. The screenshot below shows an example of both.

How to unit test in python (9)

Building a strong foundation with unit tests

Unit tests are an essential part of the test pyramid. Testing individual features and functions is important because they are often the fastest to build and run. This means that a large number of tests can be carried out extremely quickly to confirm that all requirements and acceptance criteria are met. To instill confidence in our projects from the start, unit tests should be written before any functional code.

This blog post was created as part of MattermostCommunity Writing Programand was published under reference noCC BY-NC-SA 4.0-license. For more information about the Mattermost Community Writing Program,look.


How to unit test in python? ›

Put the body of the function in a try / except block which does not return anything and return true if successful. This does not break the existing code.

How do I unit test my Python code? ›

Using Unittest
  1. Firstly, we have to import unittest as standard.
  2. Create a class called TestAdd that inherits from the TestCase class.
  3. Change the test functions into methods.
  4. Change the assertions to use the self. assertEqual() method in the TestCase class. ...
  5. Change the command-line entry point to call unittest.main()
Apr 29, 2022

How do you write a unit test effectively? ›

  1. Test Small Pieces of Code in Isolation. ...
  2. Follow Arrange, Act, Assert. ...
  3. Keep Tests Short. ...
  4. Make Them Simple. ...
  5. Cover Happy Path First. ...
  6. Test Edge Cases. ...
  7. Write Tests Before Fixing Bugs. ...
  8. Make Them Performant.

How do you test a function that does not return anything? ›

Put the body of the function in a try / except block which does not return anything and return true if successful. This does not break the existing code.

How do you increase coverage in unit testing Python? ›

Enhance your python unit testing using Coverage
  1. Use to ensure that every bit of your python code is covered by a test.
  2. Create test functions for a python class, one method and a time.
  3. Cover different aspects of your code and use the cool web interface of to monitor your progress.

What are the 4 types of testing in Python 3? ›

There are four different types of tests, each depending on the granularity of code being tested, as well as the goal of the test.
  • Unit Tests. This tests specific methods and logic in the code. ...
  • Feature Tests. This tests the functionality of the component. ...
  • Integration Tests. ...
  • Performance Tests.

How to use pytest in Python? ›

Pytest supports several ways to run and select tests from the command-line.
  1. Run tests in a module. pytest
  2. Run tests in a directory. pytest testing/
  3. Run tests by keyword expressions. pytest -k "MyClass and not method"
  4. Run tests by marker expressions. pytest -m slow.
  5. Run tests from packages.

How much unit testing is enough? ›

While there is no standard for unit testing, one number often cited in the testing world is 80%. "Eighty percent is what I usually see as the gating standard for code coverage in corporate shops," said Tim Ottinger, a senior consultant at Industrial Logic. "Any higher or lower than that is unusual."

What makes code difficult for unit testing? ›

Unit testing requires testable code

There are different types of code. For example, some classes are small and contain short methods that have simple logic. On the other hand, some code is only functional after the application is deployed to the cloud, where it talks to the database and other services.

How to study for a unit test in one day? ›

These are our top tips for studying the day before an exam:
  1. Wake up early. ...
  2. Choose the right place to work. ...
  3. Go to the library prepared. ...
  4. Create a plan before you start. ...
  5. Refrain from panicking. ...
  6. Use lecture slides and past papers. ...
  7. Study without technology and social media. ...
  8. Re-read your lecture notes and highlight.
Apr 25, 2023

How do you return nothing in Python? ›

In Python, it is possible to compose a function without a return statement. Functions like this are called void, and they return None, Python's special object for "nothing". Here's an example of a void function: >>> def sayhello(who): print 'Hello,', who + '!'

What is the return method in Python? ›

The Python return statement is a special statement that you can use inside a function or method to send the function's result back to the caller. A return statement consists of the return keyword followed by an optional return value. The return value of a Python function can be any Python object.

How do you test if a function has been called? ›

You can log a message when the function is called using: Debug. Log("Function called!"); You can store a bool that starts as false and set it to true when you enter the function. You can then check this bool elsewhere in code to tell whether your function has been called.

What is the best code coverage tool for Python? ›

Code Coverage Tools for Java, Python, C++, . Net
May 6, 2023

Is unit testing important in Python? ›

Unit tests are segments of code written to test other pieces of code, typically a single function or method, that we refer to as a unit. They are a very important part of the software development process, as they help to ensure that code works as intended and catch bugs early on.

What tool is test coverage in Python? › is one of the most popular code coverage tools for Python. It uses code analysis tools and tracing hooks provided in Python standard library to measure coverage. It runs on major versions of CPython, PyPy, Jython and IronPython. You can use with both unittest and Pytest.

How do you automate test cases in Python? ›

How to configure using Python?
  1. Quickly download and install Python on the OS.
  2. Install Selenium libraries in Python.
  3. Download and install Pycharm editor.
  4. Create one new project and write the Selenium test scripts.
  5. Run the test scripts and finally validate them.
May 31, 2022

What are the four 4 basic testing methods? ›

There are generally four recognized levels of testing: unit/component testing, integration testing, system testing, and acceptance testing.

What is the difference between pytest and JUnit? ›

JUnit is a simple framework to write repeatable tests. It is an instance of the xUnit architecture for unit testing frameworks. On the other hand, pytest is detailed as "A full-featured Python testing tool to help you write better programs".

What is the difference between pytest and unit test? ›

Unittest requires developers to create classes derived from the TestCase module and then define the test cases as methods in the class. Pytest, on the other hand, only requires you to define a function with “test_” prepended and use the assert conditions inside them.

Should I use pytest or unittest? ›

pytest, no contest. More compact, clearer to read and write, and with a bunch of powerful features not available (or harder to achieve) in unittest. The only projects I know of not using pytest are older ones that are “grandfathered in” to unittest.

What are the disadvantages of pytest? ›

Disadvantages of using PyTest

PyTest uses special routines to write tests which makes the tool very difficult to integrate with other frameworks. You have to rewrite the entire code for that to happen.

Is 100% unit test coverage possible? ›

No. 100% code coverage sounds like a good idea on paper, but it's difficult to achieve and can be very expensive. Developers spend too much time on unit tests that don't provide any value, and 100% code coverage can cause more issues in the code than it prevents.

Is unit testing easy? ›

Unit testing is an essential instrument in the toolbox of any serious software developer. However, it can sometimes be quite difficult to know how to write unit tests for a particular piece of code.

Why are unit tests not enough? ›

Unit tests do not check the integration between all the functional components of the application. They are, in fact, furthest from the end user experience. Today, you need to test the application end-to-end to drive quality.

What should you avoid in unit tests? ›

This article presents five pitfalls that lead to ineffective unit tests, and how you can fix them.
  • Write One Unit Test per Function. It seems very straightforward. ...
  • Write Tests Just for Code Coverage. ...
  • Heavily Rely on Mocks. ...
  • Write a Test That Never Fails. ...
  • Using Non-Deterministic Behaviour in Test.
Sep 28, 2021

How fast should unit tests be? ›

It really isn't something that a lot of people think about but over time can be come a problem that will have you regretting some of your early decisions. Typically the response I get when I ask this question is each test should take anywhere from 0.01 seconds to 1 second max to run in isolation.

Should I unit test first or code first? ›

It often makes sense to write the test first and then write as much code as needed to allow the test to pass. Doing this moves towards a practice known as Test-Driven Development (TDD).

How to memorize 100 pages in a day? ›

How To Study 100 Pages In One Day?
  1. Remove All Distractions To Stay Focused On Your Goal. ...
  2. Avoid Multitasking: Dedicate One Thing At A Time. ...
  3. Take Breaks Regularly. ...
  4. Reward Yourself For Recognizing Your Achievements And Motivating Yourself.
Jul 14, 2022

How many hours should you study for 1 unit? ›

The general rule of thumb regarding college studying is, that for each class, students should spend approximately 2-3 hours of study time for each hour that they spend in class. Non-science courses: For every 1 unit you are enrolled, you are recommended to spend approximately two hours outside of class studying.

How can I study for a test in 30 minutes? ›

Here's how to make the most of your cram session and study for your test in an hour or less.
  1. Find a Quiet Study Space.
  2. Review Your Study Guide.
  3. Crack Open the Textbook.
  4. Review Notes, Quizzes and Assignments.
  5. Quiz Yourself.
  6. Write Down Your Mnemonic Devices.
  7. Ask the Teacher for Help.
Sep 11, 2018

How to do nothing if true in Python? ›

In Python, the pass keyword is an entire statement in itself. This statement doesn't do anything: it's discarded during the byte-compile phase. But for a statement that does nothing, the Python pass statement is surprisingly useful.

What does return 1 mean in Python? ›

when you return 1, you are basically returning True as the final value of the function while return 0 is basically returning False as the final value of the function.

Why am I getting None returned in Python? ›

Because you are printing a function that contains a print() function. The output of printing print() is None. Also, the "return" statements in your function don't add anything to the code.

What does <= mean in Python? ›

Less than or equal to.

What does == mean in Python? ›

The == operator compares the value or equality of two objects, whereas the Python is operator checks whether two variables point to the same object in memory.

How do you write += in Python? ›

+= Operator Python: Numerical Example

The alternative is using a plus sign to add two values and the equals sign to assign the value to a variable. First, we declare a Python variable called a. This variable stores the value 10. Then, we use a += 7.5 to add 7.5 to the a variable.

What is mocking in Python? ›

Mocking is simply the act of replacing the part of the application you are testing with a dummy version of that part called a mock. Instead of calling the actual implementation, you would call the mock, and then make assertions about what you expect to happen.

How to mock a function in Python? ›

How do we mock in Python?
  1. Write the test as if you were using real external APIs.
  2. In the function under test, determine which API calls need to be mocked out; this should be a small number.
  3. In the test function, patch the API calls.
  4. Set up the MagicMock object responses.
  5. Run your test.
Feb 10, 2018

How do I check if a function is working in Python? ›

The isfunction() function of the inspect module can be used to determine if the variable is a function or not. It returns a boolean value True if it is a function else returns False.

What is a unit test in Python? ›

A unit test is a test that checks a single component of code, usually modularized as a function, and ensures that it performs as expected. Unit tests are an important part of regression testing to ensure that the code still functions as expected after making changes to the code and helps ensure code stability.

How do I test my code? ›

  1. Best tools for testing codes 1 – JS Bin. JS Bin is a simple JavaScript debugging tool. ...
  2. jsFiddle. ...
  3. Best tools for testing codes 3 – CSSDesk. ...
  4. WriteCodeOnline. ...
  5. Best tools for testing codes 5 – Tinkerbin. ...
  6. IDEOne. ...
  7. Best tools for testing codes 7 – Dabblet. ...
  8. CodeSandBox.
Jan 17, 2022

How do you test Python applications? ›

4 Techniques for Testing Python Command-Line (CLI) Apps

Learn 4 essential testing techniques for Python command-line applications: "lo-fi" print debugging, using a visual debugger, unit testing with pytest and mocks, and integration testing.

How to test Python code in command-line? ›

To run Python scripts with the python command, you need to open a command-line and type in the word python , or python3 if you have both versions, followed by the path to your script, just like this: $ python3 Hello World! If everything works okay, after you press Enter , you'll see the phrase Hello World!

What is unit test with example? ›

Unit testing is a software development process in which the smallest testable parts of an application, called units, are individually scrutinized for proper operation. Software developers and sometimes QA staff complete unit tests during the development process.

How do you write a unit test for a class in Python? ›

Putting it all together:
  1. The setUpClass() class method is executed before any of the tests are run.
  2. The tearDownClass() class method is executed after all the tests have run.
  3. The setUp() and tearDown() methods are executed before and after each test, respectively.
Jan 31, 2023

What is Pytest vs unit test in Python? ›

Unittest requires developers to create classes derived from the TestCase module and then define the test cases as methods in the class. Pytest, on the other hand, only requires you to define a function with “test_” prepended and use the assert conditions inside them.

How do programmers test their code? ›

The common ways of doing static testing include linting and type checking. Linting involves checking the code for programming and stylistic errors. A linter analyzes the code and flags potential errors. Examples of linting tools are EsLint, PyLint, and CSSLint.

What are the way to perform testing? ›

The following are the fundamental steps involved in testing an application:
  1. Create a test plan according to the application requirements.
  2. Develop manual test case scenarios from the end-users perspective.
  3. Automate the test scenarios using scripts.
Mar 17, 2023

What is the process of testing? ›

Testing is the process of executing a program or part of a program with the intention of finding errors. The different phases of a test life cycle are Test Planning and Control, Test Analysis and Design, Test Implementation and Execution, Evaluating Exit Criteria and Reporting, and Test Closure.

Is Python testing easy? ›

The article of an authoritative blog Automation Panda says that Python suits best for test automation – everything is simpler, clearer, easier to maintain, there are lots of libraries with ready-made solutions, and the Pytest Framework is generally perfect and quickly mastered.

How do I run a unit test in Python terminal? ›

So the command to run python unittest will be: $python3. 6 -m unittest Basic_Test. Testing If you want to see the verbose, then the command will be; $python3. 6 -m unittest -v Basic_Test.

What tools are used for unit testing in Python? ›

Let's go through the detailed of most preferred Python Testing Frameworks and understand their benefits and limitations that will help decide when to use which:
  • Behave Framework. ...
  • Lettuce Framework. ...
  • Robot Framework. ...
  • Pytest Framework. ...
  • TestProject Framework. ...
  • PyUnit (Unittest) Framework. ...
  • Testify Framework. ...
  • Doctest Framework.
Mar 18, 2023

How do I test Python code in Windows? ›

Search for cmd on the toolbar, then hit Enter. Once the command prompt is open, simply type python and hit Enter again. When you're in an interactive session, every Python statement is executed immediately and any output is displayed directly beneath.

How do I run a test from the command line? ›

Running test cases from the command prompt
  1. Run multiple test cases by providing the test cases as parameters separated by commas (,...,...).
  2. Run only the test method or test procedure in a specific test case by providing the name of the test method or test procedure separated by # with the test case name.

How do I run a Python script? ›

The most basic and easy way to run a Python script is by using the python command. You need to open a command line and type the word python followed by the path to your script file like this: python Hello World! Then you hit the ENTER button from the keyboard, and that's it.


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