Thursday, May 23, 2024
HomeWeb developmentA Information to Python Unit Testing with unittest and pytest

A Information to Python Unit Testing with unittest and pytest

On this article, we’ll have a look at what software program testing is, and why it is best to care about it. We’ll discover ways to design unit checks and write Python unit checks. Particularly, we’ll have a look at two of essentially the most used unit testing frameworks in Python, unittest and pytest.

Introduction to Software program Testing

Software program testing is the method of analyzing the conduct of a software program product to guage and confirm that it’s coherent with the specs. Software program merchandise can have hundreds of strains of code, and a whole bunch of elements that work collectively. If a single line doesn’t work correctly, the bug can propagate and trigger different errors. So, to make sure that a program acts because it’s purported to, it needs to be examined.

Since trendy software program could be fairly difficult, there are a number of ranges of testing that consider totally different elements of correctness. As acknowledged by the ISTQB Licensed Check Basis Degree syllabus, there are 4 ranges of software program testing:

  1. Unit testing, which checks particular strains of code
  2. Integration testing, which checks the mixing between many items
  3. System testing, which checks your entire system
  4. Acceptance testing, which checks the compliance with enterprise objectives

On this article, we’ll speak about unit testing, however earlier than we dig deep into that, I’d wish to introduce an vital precept in software program testing.

Testing reveals the presence of defects, not their absence.

ISTQB CTFL Syllabus 2018

In different phrases, even when all of the checks you run don’t present any failure, this doesn’t show that your software program system is bug-free, or that one other check case received’t discover a defect within the conduct of your software program.

What’s Unit Testing?

That is the primary stage of testing, additionally referred to as part testing. On this half, the one software program elements are examined. Relying on the programming language, the software program unit is perhaps a category, a operate, or a technique. For instance, if in case you have a Java class referred to as ArithmeticOperations that has multiply and divide strategies, unit checks for the ArithmeticOperations class might want to check each the right conduct of the multiply and divide strategies.

Unit checks are often carried out by software program testers. To run unit checks, software program testers (or builders) want entry to the supply code, as a result of the supply code itself is the thing below check. Because of this, this method to software program testing that checks the supply code straight is known as white-box testing.

You is perhaps questioning why it is best to fear about software program testing, and whether or not it’s value it or not. Within the subsequent part, we’ll analyze the motivation behind testing your software program system.

Why it is best to do unit testing

The principle benefit of software program testing is that it improves software program high quality. Software program high quality is essential, particularly in a world the place software program handles all kinds of our on a regular basis actions. Bettering the standard of the software program continues to be too imprecise a aim. Let’s attempt to specify higher what we imply by high quality of software program. In keeping with the ISO/IEC Commonplace 9126-1 ISO 9126, software program high quality contains these components:

  • reliability
  • performance
  • effectivity
  • usability
  • maintainability
  • portability

For those who personal an organization, software program testing is an exercise that it is best to think about fastidiously, as a result of it may have an effect on your enterprise. For instance, in Could 2022, Tesla recalled 130,000 automobiles because of a difficulty in automobiles’ infotainment methods. This subject was then fastened with a software program replace distributed “over the air”. These failures value money and time to the corporate, they usually additionally prompted issues for the purchasers, as a result of they couldn’t use their automobiles for some time. Testing software program certainly prices cash, however it’s additionally true that firms can save tens of millions in technical assist.

Unit testing focuses on checking whether or not or not the software program is behaving accurately, which suggests checking that the mapping between the inputs and the outputs are all achieved accurately. Being a low-level testing exercise, unit testing helps within the early identification of bugs in order that they aren’t propagated to larger ranges of the software program system.

Different benefits of unit testing embody:

  • Simplifying integration: by guaranteeing that every one the elements work properly individually, it’s simpler to resolve integration issues.
  • Minimizing code regression: with a very good quantity of check circumstances, if some modifications to the supply code sooner or later will trigger issues, it’s simpler to find the difficulty.
  • Offering documentation: by testing the right mapping between enter and output, unit checks present documentation on how the strategy or class below check works.

Designing a Check Technique

Let’s now have a look at design a testing technique.

Definition of check scope

Earlier than beginning to plan a check technique, there’s an vital query to reply. What components of your software program system do you wish to check?

It is a essential query, as a result of exhaustive testing is unimaginable. Because of this, you’ll be able to’t check each attainable enter and output, however it is best to prioritize your checks based mostly on the dangers concerned.

Many components have to be taken into consideration when defining your check scope:

  • Danger: what enterprise penalties would there be if a bug have been to have an effect on this part?
  • Time: how quickly would you like your software program product to be prepared? Do you will have a deadline?
  • Finances: how a lot cash are you keen to spend money on the testing exercise?

When you outline the testing scope, which specifies what it is best to check and what you shouldn’t check, you’re prepared to speak concerning the qualities {that a} good unit check ought to have.

Qualities of a unit check

  • Quick. Unit checks are largely executed robotically, which suggests they have to be quick. Gradual unit checks usually tend to be skipped by builders as a result of they don’t present immediate suggestions.
  • Remoted. Unit checks are standalone by definition. They check the person unit of code, they usually don’t rely on something exterior (like a file or a community useful resource).
  • Repeatable. Unit checks are executed repeatedly, and the end result have to be constant over time.
  • Dependable. Unit checks will fail provided that there’s a bug within the system below check. The atmosphere or the order of execution of the checks shouldn’t matter.
  • Named correctly. The title of the check ought to present related details about the check itself.

There’s one final step lacking earlier than diving deep into unit testing in Python. How will we set up our checks to make them clear and simple to learn? We use a sample referred to as Organize, Act and Assert (AAA).

The AAA sample

The Organize, Act and Assert sample is a standard technique used to write down and set up unit checks. It really works within the following method:

  • In the course of the Organize part, all of the objects and variables wanted for the check are set.
  • Subsequent, in the course of the Act part, the operate/methodology/class below check is known as.
  • Ultimately, in the course of the Assert part, we confirm the end result of the check.

This technique gives a clear method to organizing unit checks by separating all the primary components of a check: setup, execution and verification. Plus, unit checks are simpler to learn, as a result of all of them comply with the identical construction.

Unit Testing in Python: unittest or pytest?

We’ll now speak about two totally different unit testing frameworks in Python. The 2 frameworks are unittest and pytest.

Introduction to unittest

The Python customary library contains the unittest unit testing framework. This framework is impressed by JUnit, which is a unit testing framework in Java.

As acknowledged within the official documentation, unittest helps a couple of vital ideas that we’ll point out on this article:

  • check case, which is the one unit of testing
  • check suite, which is a bunch of check circumstances which are executed collectively
  • check runner, which is the part that may deal with the execution and the results of all of the check circumstances

unittest has its approach to write checks. Particularly, we have to:

  1. write our checks as strategies of a category that subclasses unittest.TestCase
  2. use particular assertion strategies

Since unittest is already put in, we’re prepared to write down our first unit check!

Writing unit checks utilizing unittest

Let’s say that now we have the BankAccount class:

import unittest

class BankAccount:
  def __init__(self, id): = id
    self.steadiness = 0

  def withdraw(self, quantity):
    if self.steadiness >= quantity:
      self.steadiness -= quantity
      return True
    return False

  def deposit(self, quantity):
    self.steadiness += quantity
    return True

We are able to’t withdraw more cash than the deposit availability, so let’s check that this situation is dealt with accurately by our supply code.

In the identical Python file, we are able to add the next code:

class TestBankOperations(unittest.TestCase):
    def test_insufficient_deposit(self):
      a = BankAccount(1)
      end result = a.withdraw(200)
      self.assertFalse(end result)

We’re creating a category referred to as TestBankOperations that’s a subclass of unittest.TestCase. On this method, we’re creating a brand new check case.

Inside this class, we outline a single check operate with a technique that begins with check. That is vital, as a result of each check methodology should begin with the phrase check.

We count on this check methodology to return False, which implies that the operation failed. To claim the end result, we use a particular assertion methodology referred to as assertFalse().

We’re able to execute the check. Let’s run this command on the command line:

python -m unittest

Right here, is the title of the file containing all of the supply code. The output ought to look one thing like this:

Ran 1 check in 0.001s


Good! Which means that our check was profitable. Let’s see now how the output seems to be when there’s a failure. We add a brand new check to the earlier class. Let’s attempt to deposit a adverse amount of cash, which after all isn’t attainable. Will our code deal with this situation?

That is our new check methodology:

  def test_negative_deposit(self):
    a = BankAccount(1)
    end result = a.deposit(-100)
    self.assertFalse(end result)

We are able to use the verbose mode of unittest to execute this check by placing the -v flag:

python -m unittest -v

And the output is now totally different:

test_insufficient_deposit (instance.TestBankOperations) ... okay
test_negative_deposit (instance.TestBankOperations) ... FAIL

FAIL: test_negative_deposit (instance.TestBankOperations)
Traceback (most up-to-date name final):
  File "", line 35, in test_negative_deposit
    self.assertFalse(end result)
AssertionError: True is just not false

Ran 2 checks in 0.002s

FAILED (failures=1)

On this case, the verbose flag provides us extra data. We all know that the test_negative_deposit failed. Particularly, the AssertionError tells us that the anticipated end result was purported to be false however True is just not false, which implies that the strategy returned True.

The unittest framework gives totally different assertion strategies, based mostly on our wants:

  • assertEqual(x,y), which checks whether or not x == y
  • assertRaises(exception_type), which checks if a particular exception is raised
  • assertIsNone(x), which checks if x is None
  • assertIn(x,y), which checks if x in y

Now that now we have a fundamental understanding of write unit checks utilizing the unittest framework, let’s take a look on the different Python framework referred to as pytest.

Introduction to pytest

The pytest framework is a Python unit testing framework that has a couple of related options:

  • it permits advanced testing utilizing much less code
  • it helps unittest check suites
  • it presents greater than 800 exterior plugins

Since pytest isn’t put in by default, now we have to put in it first. Be aware that pytest requires Python 3.7+.

Putting in pytest

Putting in pytest is kind of straightforward. You simply should run this command:

pip set up -U pytest

Then test that every little thing has been put in accurately by typing this:

pytest --version

The output ought to look one thing like this:

pytest 7.1.2

Good! Let’s write the primary check utilizing pytest.

Writing unit checks utilizing pytest

We’ll use the BankAccount class written earlier than, and we’ll check the identical strategies as earlier than. On this method, it’s simpler to check the trouble wanted to write down checks utilizing the 2 frameworks.

To check with pytest we have to:

  • Create a listing and put our check recordsdata inside it.
  • Write our checks in recordsdata whose names begin with test_ or finish with pytest will search for these recordsdata within the present listing and its subdirectories.

So, we create a file referred to as and we put it right into a folder. That is what our first check operate seems to be like:

def test_insufficient_deposit():
  a = BankAccount(1)
  end result = a.withdraw(200)
  assert end result == False

As you will have seen, the one factor that modified with respect to the unittest model is the assert part. Right here we use plain Python assertion strategies.

And now we are able to take a look on the file:

class BankAccount:
  def __init__(self, id): = id
    self.steadiness = 0

  def withdraw(self, quantity):
    if self.steadiness >= quantity:
      self.steadiness -= quantity
      return True
    return False

  def deposit(self, quantity):
    self.steadiness += quantity
    return True

def test_insufficient_deposit():
  a = BankAccount(1)
  end result = a.withdraw(200)
  assert end result == False

To run this check, let’s open a command immediate contained in the folder the place the file is positioned. Then, run this:


The output might be one thing like this:

======== check session begins ======== 
platform win32 -- Python 3.7.11, pytest-7.1.2, pluggy-0.13.1
rootdir: folder
plugins: anyio-2.2.0
collected 1 merchandise .                                                                                                   [100%]

======== 1 handed in 0.02s ======== 

On this case, we are able to see how straightforward it’s to write down and execute a check. Additionally, we are able to see that we wrote much less code in comparison with unittest. The results of the check can be fairly straightforward to grasp.

Let’s transfer on to see a failed check!

We use the second methodology we wrote earlier than, which is known as test_negative_deposit. We refactor the assert part, and that is the end result:

def test_negative_deposit():
  a = BankAccount(1)
  end result = a.deposit(-100)
  assert end result == False

We run the check in the identical method as earlier than, and this must be the output:

======= check session begins =======
platform win32 -- Python 3.7.11, pytest-7.1.2, pluggy-0.13.1
rootdir: folder
plugins: anyio-2.2.0
collected 2 objects .F                                                                                                  [100%]

======= FAILURES =======
_____________ test_negative_deposit _____________
    def test_negative_deposit():
      a = BankAccount(1)
      end result = a.deposit(-100)
>     assert end result == False
E     assert True == False AssertionError
======= brief check abstract data =======
FAILED - assert True == False
======= 1 failed, 1 handed in 0.15s =======

By parsing the output, we are able to learn collected 2 objects, which implies that two checks have been executed. Scrolling down, we are able to learn {that a} failure occurred whereas testing the test_negative_deposit methodology. Particularly, the error occurred when evaluating the assertion. Plus, the report additionally says that the worth of the end result variable is True, so which means that the deposit methodology accommodates an error.

Since pytest makes use of the default Python assertion key phrase, we are able to examine any output we get with one other variable that shops the anticipated end result. All of this with out utilizing particular assertion strategies.


To wrap it up, on this article we lined the fundamentals of software program testing. We found why software program testing is crucial and why everybody ought to check their code. We talked about unit testing, and design and implement easy unit checks in Python.

We used two Python frameworks referred to as unittest and pytest. Each have helpful options, they usually’re two of the most-used frameworks for Python unit testing.

Ultimately, we noticed two fundamental check circumstances to present you an concept of how checks are written following the Organize, Act and Assert sample.

I hope I’ve satisfied you of the significance of software program testing. Select a framework comparable to unittest or pytest, and begin testing — as a result of it’s value the additional effort!

For those who loved this text, you may additionally discover the next helpful:



Please enter your comment!
Please enter your name here

Most Popular

Recent Comments