What Is Unit Testing_ A Complete Guide With Examples.pdf

What Is Unit Testing: A Complete
Guide With Examples
Testing is one of the most important components of any software
development lifecycle. The more frequently you test, the earlier you
catch any bugs, and the more reliable your software product becomes.
However, repeatedly testing it can be time-consuming, especially
considering all the different operating scenarios it can use or the
number of external dependencies involved.
Instead, most developers opt for unit testing, where—as the name
suggests — you independently test each part of your software product
to see that it’s working correctly before putting it all together.
In this guide, we’ll dive deep into what unit testing looks like and how
to get started.

What Is Unit Testing?
Unit testing refers to a software development practice in which you
test each unit of an application separately.
In this scenario, a unit could refer to a function, procedure, class, or
module—essentially, it’s the smallest testable part of the software. Unit
testing ensures it works as it should before the entire system is
integrated.
It’s vital to have unit tests that run speedily, are isolated from external
dependencies, and are easy to automate for accuracy and
convenience.
Developers could choose to manually write and execute their own unit
test cases, which is often ideal for smaller projects or situations that
call for more hands-on examination of the code.
However, automation is generally preferred to ensure that unit tests
run efficiently, consistently, and at scale. Automated testing
frameworks like JUnit, NUnit, and PyTest are commonly used to
streamline this process.
When Should Unit Testing Be Performed, and by
Whom?
Unit testing is typically the first level of software testing and is
performed before integration testing, acceptance testing, and system
testing. This helps identify any issues with the codebase before too
much time is invested in building the full features.

Developers will typically write the unit tests, as they’re the ones who
know best how any individual class or function should work. A lot of
the time, they’ll run these tests themselves since each test takes a
negligible amount of time.
However, in some cases, they’ll opt to hand it over to the Quality
Assurance (QA) process team instead. In general, unit testing can be
handled by any team member with access to the software’s source
code and a good understanding of its structure and functionality.
Benefits of Unit Testing
As the first layer of testing, performing unit tests is key to building and
delivering a robust software product. Simply put, if your individual units
aren’t working as they should, they certainly won’t work together. The
benefits of unit testing include:
1. Better code writing
Unit testing, by nature, calls for each component of the software to
have a properly defined responsibility that you can test in isolation.
This motivates developers to write high-quality code that’s easy to
maintain.
2. Early bug detection
Running unit tests helps detect bugs early in software development
and pinpoint exactly where the bug lies. This allows you to fix it faster
and avoid bigger problems later when dependencies among different
software product components become more complex.

3. Documented results
Unit tests are ideal for chalking out your software’s logic, as they
demonstrate exactly what behavior you expect from each component.
This is great for knowledge transfer, regression prevention, and as a
standard for future software products you develop.
4. Less need for regression testing
Regression testing involves retesting the software as a whole for
functionality and reliability after changes are incorporated. This can be
time-consuming and expensive. However, with unit testing,
functionality is verified from the get-go, making regression tests much
shorter and easier to run.
5. Better overall development process
Businesses that incorporate unit testing enjoy a more robust
development lifecycle, one that fixes issues as early as possible.
Moreover, developers are motivated to write code that can be
repeatedly run without difficulty, making for a more agile coding
process.
Anatomy of a Unit Test
There are five main aspects of a unit test:
1. Test fixtures
Also known as test context, test fixtures are the components of a test
case that create the initial conditions for executing the test in a
controlled fashion.

These ensure that you have a consistent environment to repeat your
testing in (such as configuration settings, user account, sandbox
environment, etc.), which is important when you’re testing the same
feature over and over to get it just right.
2. Test case
This is a piece of code that determines the behavior of another piece
of code. Developers need to define exactly what they expect from any
unit in terms of results—the test case ensures that the unit produces
exactly those results.
3. Test runner
This is a framework that enables the execution of multiple tests at the
same time by quickly scanning your directories or codebase to file and
execute the right tests.
A test runner can also run tests by priority, manage the test
environment to be free of any external dependencies, and provide you
with a core analysis of the test results.
4. Test data
This refers to the data you select to run a test on your chosen unit.
The goal is to choose data that covers as many possible scenarios
and outcomes for that unit as possible. Common examples include:
● Normal cases: regular input values within acceptable limits
● Boundary cases: values at the boundaries of the acceptable
limits

● Corner cases: values that represent extreme or unusual
scenarios that could affect your unit or even your whole system
● Invalid/error cases: input values that fall outside the valid
range, used to assess how the unit responds, including any error
handling or messages
5. Mocking and stubbing
In most unit tests, developers focus on the specific unit. However, in
some cases, your test will call for two units, especially if there are any
necessary dependencies. Mocking and stubbing serve as substitutes
for those dependencies so that your unit can still be tested in isolation.
For instance, you might have a ‘user’ class that depends on an
external ‘email sender’ class for delivering email notifications. In that
case, developers can create a mock object of the ‘email sender class’
to test the behavior of the ‘user’ class without actually sending
anybody any emails.
How to Do a Unit Test
The basic procedure for running a unit test involves the following
steps:
1. Identify the unit to test
Decide which specific code unit you’ll be testing: a method, a class, a
function, or anything else. Study the code, decide on the logic needed
to test it, and list the test cases you plan to cover.
2. Use high-quality test data

You should always run your tests with data as similar to what the
software product will work with in real life as possible. Be sure to cover
edge cases and invalid data as well to see how your units function
under those circumstances.
Also, avoid hard-coding data into your test cases, as this makes them
harder to maintain.
3. Choose between manual and automated testing
As the name suggests, manual testing requires developers to
manually run the code to see if your unit is behaving as expected. For
automated testing, they’ll write a script that automates the code
interactions.
Both have their uses—automated testing lets you cover more ground
faster, but manual testing is a more hands-on option for situations that
require a more creative or intuitive perspective.
4. Prepare your test environment
This involves preparing your test data, any mock objects, and all the
necessary configurations and preconditions for unit testing. Ideally,
you’ll also want to isolate the code in a dedicated testing environment
to keep the test free of any external dependencies.
5. Write and run the test
If you’re using an automated testing approach, start by writing a script
for a test runner. You can create test cases before you write the actual

code. This will help you keep any gaps in logic or software
requirements before you invest time and effort in writing the code.
Then, run your tests. Cover all the test cases you listed in the previous
steps. Ensure you reset the test conditions before each run of your
unit test, and try to avoid any dynamically generated data that could
negatively affect test results.
6. Evaluate your result and make any fixes required
Wherever your tests fail, evaluate where the problem lies and tweak
the code. Then, the tests will be rerun to verify that the new code has
solved the problem. This could take some time, which is why it’s
necessary to account for a buffer period in the software development
lifecycle.
Unit Testing Types
Popular unit testing techniques include:
1. Black box testing
This form of unit test focuses on the unit’s external functionality and
behavior, ignoring its internal structure.
Your team will draft test cases based on the unit specifications and the
expected inputs and outputs. For instance, they might test a login
function by inputting different sets of valid and invalid credentials to
see if it behaves correctly.
2. White box testing
If you want to consider the internal structure and implementation, with
test cases designed to cover all the code branches and segments in

the unit, consider white box testing. This includes testing all possible
execution paths in the code, such as each branch of an if-else
statement, to ensure every possible condition is tested and behaves
as expected.
3. Grey box testing
This is also known as semi-transparent testing. In this case, the
testers only have partial awareness of the unit’s internal details. It
includes pattern testing, orthogonal pattern testing, matrix testing, and
regression testing.
In a unit test example, you can use partial knowledge of the database
schema to test how the system handles specific query inputs.
4. Code coverage testing
Code coverage testing involves measuring the extent to which the
code has been tested by techniques such as statement coverage,
decision coverage, and branch coverage. This helps identify untested
code sections and increases the thoroughness of your unit tests. For
instance, you could run tests to ensure every line of code in a function
has been executed at least once.
The Unit Testing Life Cycle
Here’s what the basic unit testing life cycle looks like:
● Review the code written after you implement your test.
● Refactor the test and make suitable changes to the code based
on the insights you received about what’s happening with it.
● Execute the test with suitable input values and compare the
actual results with the expected ones.

● Fix any bugs detected during the testing process. This helps you
prepare code that’s as clean as possible before you send it into
production.
● Re-execute your tests to verify the results after you’ve made the
changes. This helps you keep track of everything you have done
and ensure that the changes haven’t led to regressions in the
existing functionality.
The Role of Unit Testing in a QA Strategy
Unit testing helps provide developers with feedback as early on in the
development process as possible. They get exact reports on where
bugs lie and, thus, where to concentrate their efforts.
At the same time, unit testing alone isn’t enough, as it doesn’t validate
how the units integrate with other units. Despite its many advantages,
it does have some limitations:
● It only tests the functional attributes of your code
● It cannot detect all errors related to interface or integration
● Writing high-quality unit tests can be challenging and
time-consuming
● It’s not ideal for testing your app’s UI, as that requires a lot of
human intuition and hands-on testing to get it right
You thus need to follow up your unit testing with various other types of
testing, including integration testing, end-to-end testing, performance
testing, and so on.
Top Open-Source Unit Testing Tools of 2024

Let’s look at a few popular open-source options for conducting unit
tests:
1. JMockit
JMockit is a unit testing tool that offers a comprehensive set of APIs
and functionalities for integration with TestNG and the JUnit
framework.
One of its standout features is its support for three types of code
coverage: line coverage, path coverage, and data coverage. This
allows you to gain deeper insights into how much of your code is
exercised during tests and ensures all critical paths are covered.
JMockit also excels in its verification capabilities. You can capture
instances of objects and mock implementations as your test runs,
even if you don’t have direct knowledge of the actual implementation
classes.

2. Emma
Emma is a toolkit specifically built to calculate Java code coverage. It
does not depend on external libraries or require access to source
code.
You can integrate it into your existing Java projects without additional
setup overhead. Emma also provides reports in various formats, such
as text, HTML, and XML, which can be easily shared with all the
software project stakeholders.
You can also specify threshold values for coverage using Emma. Any
items that fall below these levels are highlighted in the output reports,
giving you quick visibility into parts of the code that need more testing.
3. SimpleTest
SimpleTest is a unit testing framework tailored for PHP apps. It allows
you to create and organize test cases using its built-in base test

classes, from which your test case classes and methods are
extended.
A key feature of SimpleTest is its support for SSL, forms, and basic
authentication. You can simulate interactions with secure web pages,
handle form submissions, or work through proxies with little additional
configuration.
It also simplifies test execution with its autorun.php file, which
automatically converts test cases into executable test scripts.
4. Typemock Isolator
Typemock Isolator is a unit testing mocking solution primarily
developed for the .NET. It reduces the time spent on bug fixing by
automating much of the testing process, enabling you to focus more
on feature development and less on debugging.

The tool is easy to integrate, offering a simple API that doesn’t require
modifications to existing legacy code. This makes it particularly useful
for projects where refactoring isn’t feasible. You can implement unit
tests without disrupting the existing codebase.
Typemock Isolator is written in C and C++ and designed for Windows
environments. It ensures close integration with system-level
operations.
Unit Testing Best Practice
As you continue to run unit tests, you’ll learn to get faster and more
accurate. Here are some best practices to help you out:
1. Make sure your tests are fast and simple
Most of the time, you’ll be running a large number of unit tests for any
software product. If they take too much time to run, developers might
hesitate to do so on the grounds that it would slow down the process.
By having short and to-the-point unit tests, they can quickly verify that
their code is correct before proceeding.
The best way to ensure this is to have each unit test focus on one
particular functionality or behavior. Give each test a simple yet
descriptive name and structure it according to the AAA pattern for
optimum clarity.
For example, you could have a test named
‘Test_AdditionOfTwoNumbers_ReturnsCorrectSum,’ which focuses

solely on verifying the behavior of a function that adds two numbers,
structured in the Arrange-Act-Assert (AAA) pattern.
2. Check for consistency
Your tests should always give you consistent results, regardless of
what order you run the tests in or what changes you make to the code
in between each test run. For example, a test for a function that
calculates the area of a rectangle should return the same result every
time, regardless of whether it runs before or after other tests.
3. Keep refactoring your tests as needed
Remember to refactor your test for maintainability and readability as
needed, just as you’d regularly update your production code.
In a unit testing example, if you initially wrote a test with hardcoded
values like ‘Test_AdditionOfNumbers_2Plus3_Returns5,’ you could
refactor it to use parameters such as
‘Test_AdditionOfNumbers_WithValidInputs_ReturnsCorrectSum’ to
make it reusable for multiple input cases.
4. Incorporate tests into your CI pipeline
Automate your unit tests and incorporate them into your continuous
integration (CI) pipeline, ensuring that tests run on every commit or
pull request to provide timely feedback and detect potential issues
early.

Conclusion
Unit testing isn’t just another box to check off in software
development; it’s your safety net for making sure each part of your
code does exactly what you expect.
Over time, these tests become like living documentation, helping you
catch issues early and avoid those frustrating, hard-to-find software
bugs.

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