What Is Unit Testing? Frameworks, Examples, and Best Practices

What Is Unit Testing? Frameworks, Examples, and Best Practices

If you have a software development project, it’s a good idea to ensure the coding is correct and will perform as required, catching and fixing errors early—helping save time and money.

That’s why it’s important to include unit testing in the software development workflow—some might even insist it’s an essential safeguard for any large software development project.

Read on to find out more about the importance of software unit test runs. We’ll cover:

What is unit testing?

Unit testing is performed during the coding stage of a software development project to test individual units of the application. It’s designed to test that each unit of the software code performs as required. A unit might be a class or class method in object-oriented languages and a procedure or function in procedural and functional software languages.

Unit tests need to run quickly, so they run in isolation without external processes or systems.

What is the importance and the benefit of unit testing?

Writing software unit test code provides quick, almost instantaneous feedback about the correctness of the coding, including its design and implementation. Test passes and test fails confirm if the software works or doesn’t work as intended and can update its vetting every time someone changes a specific piece of code.

Unit testing saves time and money by fixing problems early in the development process, as opposed to later during system testing, integration testing, and even beta testing.

Other benefits of unit testing include:

  • It gives developers insight into the testing code base, so they can make any code changes quickly.
  • More bugs caught early in the process enables the development team to spend less time debugging later and more time creating value with their work.
  • New team members can get up to speed more easily, without having to worry about damaging existing code, because any problems will be caught quickly.
  • A well-constructed unit test can be used as documentation, which is updated each time the test is run.
  • Because each unit test is a standalone function, it can test different parts of a project without waiting for others to be completed.
  • Catching errors while working on part of a project makes it easier to solve problems quickly since you’re already focused on the task.

Unit testing vs. integration tests

The purpose of a unit test is to validate a specific, independent unit of software. By contrast, an integration test considers how different parts of a system work together. It validates complex scenarios that usually require external resources, such as databases or web servers.

An integration test combines software modules into a group and checks how they work together. Other features of an integration test include:

  • It’s done after unit testing and before system testing.
  • It pays close attention to the integration of software modules.
  • It verifies that code works well with external dependencies.

Unit tests check that each individual part of the program is correct. Other features include:

  • It can be performed anytime during development.
  • It only checks that each unit performs as expected and doesn’t look for systemwide or integration issues.
  • It’s usually executed by the developer.
  • It doesn’t check external dependencies.
  • A unit test is inexpensive to maintain.

Unit testing, integration testing, and end-to-end testing

While a unit test tests different modules of a program in isolation, an integration tests interaction with dependencies (usually by simulating those dependencies), and end-to-end testing tests the live product.

Unit testing separates the testable parts of an application programming interface (API) and verifies if they work properly on their own. Other unit test features include:

  • It’s a white box testing technique.
  • It’s written by software developers.
  • It has a higher number of test cases than other types of testing.
  • It has a low cost to maintain.
  • It has high rates of change.

Integration testing combines different units to verify they work together as required. It also:

  • Finds errors in the interface between modules.
  • Helps modules interact with third-party tools, including APIs.
  • Improves reliability of tests and improves test coverage.

End-to-end testing tests the entire software product from beginning to finish. It helps to:

  • Ensure a bug-free product in the market.
  • Reduce development time.
  • Keep costs under control.

4 most common unit testing techniques

The following unit testing techniques focus on how a piece of software works according to its internal structure and technologies, purely from a performance point of view, or combining the different approaches.

Black box testing

With a black box test, software developers test the functionalities of a program without knowing anything about its internal structure. The testers know nothing about the code’s technological background but only about its expected behaviors, and they want to ensure these are carried out accurately and efficiently

For example, Dynamic Application Security Testing (DAST) is a black box test for products in staging or production, providing feedback on security and compliance issues.

White box testing

White box testing, also known as clear box testing, is a software testing process that demands a detailed knowledge of the internal code structure of a software program to determine if it’s performing its intended function and how it’s performing this function.

Usually, those who perform white box testing are software developers or engineers who have worked on the code and know its internal structure and technologies.

Unit testing is a type of white box testing where the programmer examines their lines of coding to identify bugs early in the development process.

Gray box testing

Gray box or grey box testing, also known as translucent testing, is a method in which testers have only limited knowledge of the internal structure of an application. It’s designed to identify problems because of improper code structure or incorrect use of the code.

One purpose of this method is to test things from a user’s perspective rather than the designer’s, giving the tester enough time to fix bugs if they pop up. For example, if a tester clicks a malfunctioning link in a website design, they can make the appropriate HTML code adjustments.

Types of gray box testing include:

  • Matrix testing
  • Regression testing
  • Pattern testing

Code coverage testing techniques

Code coverage testing is used to determine how well the code is covered by the unit tests. Some possible metrics used in code coverage testing include:

  • Statement coverage: This is the number of statements in the program that have been executed.
  • Decision or branch coverage: This is a testing method that aims to ensure each branch from each decision point is executed a minimum of one time.
  • Condition coverage: This is the number of boolean sub-expressions that have been tested for true and false values.
  • Finite coverage: This works based on how frequent visits are from static states and other transactions.

Unit testing best practices

To get the most out of unit testing, here are some best practices that range from embracing simplicity to developing a fast-testing structure and consistent naming convention.

Only test one code

When writing unit tests, make sure they are designed to test one thing at a time, isolating a unit and making sure it works. While there are tests that tackle more than one unit at a time, these are called integration tests.

Ensure that tests are not complex

The more complex a testing code is, the more likely it will have bugs. If one of your goals is to keep the app development code simple, the unit testing code should be the same. Keeping its cyclomatic complexity low is one good practice.

Create consistent naming

Consider adopting a consistent naming convention that makes sense for the development team. It should be easy to understand, remember, and convey what the test method is about.

Develop a fast-testing structure

A unit test should be developed to run quickly, preferably measured in milliseconds rather than seconds. If they go longer, developers will be reluctant to use them, which defeats the purpose of having this safety net in place.

Remember tests should be reliable

Unit test codes must be reliable or else they defeat the purpose. As stated, keep them simple and use clear standard naming conventions to help prevent mistakes. Unit test fails shouldn’t happen because they’re written by the developer, who has detailed knowledge of the inner workings of how a feature was implemented. The test otherwise might fail because of requirement changes or implementation problems.

Tests should have clear outcomes and next steps

A good unit test must have an expected outcome and an actual outcome. How is the code supposed to function, and how does this differ during the testing? By seeing how reality differs from expectation, which offers a clear pathway for fixing bugs and problems so that the two are aligned.

Unit testing tools and frameworks

Many automatic software unit testing tools are designed for different programming languages and offer different bells and whistles. The tools and frameworks offer developers a way (often through assert statements or method attributes) to show whether the test method has passed or failed.

The tools and frameworks—including mocking/stubbing frameworks—provide what developers should know when creating unit tests, such as:

  • Ways to verify the effects of the action they want to take
  • Code attributes providing tests with test data
  • Enabling a test runner to run automated tests embedded in the code, reporting the results

Unit tests can be manual or automated. The latter is usually preferred because it saves time and effort. There are a lot of online tutorials to help you learn different frameworks and tools. Unit test code templates are also available.

Popular tools and frameworks include:


JUnit is an open-source unit testing framework designed to help Java developers write and run repeatable tests. Its reliability is based on the fact that it finds bugs early in code writing and is useful in test-driven development environments.

JUnit 5 is the next generation of JUnit, which is designed to create an up-to-date foundation for developer-side testing on the Java Virtual Machine (JVM).


JMockit is an open-source tool for unit testing that has a collection of tools and APIs, enabling developers to write tests using TestNG or JUnit. Its features include out-of-container integration testing for Java EE and Spring-based apps, mocking API with recording and verification syntax, faking API for replacing implementations, and a code coverage tool.


Developed by Parasoft, Jtest is often used for testing Java applications and supports static code analysis. It claims that its tools will “ensure defect-free coding through every stage of software development in the Java environment.” It ensures that Java code complies with industry security standards and achieves code coverage targets by creating an optimized suite of JUnit tests.


TestNG is a testing framework inspired by JUnit and NUnit, but with some added functionalities. It supports parameterized and data-driven testing, as well as unit, functional, and continuous integration testing. It’s also supported by a variety of tools and plugins, such as Eclipse, IDEA, and Maven.


Quilt is a Java software development tool that measures coverage — “the extent to which unit testing exercises the software under test.” It’s a free, cross-platform-based software optimized for use with the JUnit unit test package, the Ant Java build facility, and the Maven project management toolkit. It doesn’t work on source code but just manipulates the classes and machine code of JVM.


NUnit is a widely used open-source tool that works with all .NET languages and supports writing scripts manually (but not automatically) and data-driven tests that can run in parallel. Initially ported from JUnit, Version 3 has been completely rewritten with a lot of new features and support for a wide range of .NET platforms. Different NUnit packages have been downloaded over 126 million times on NuGet.org.


EMMA is a free, open-source set of tools for analyzing and measuring Java code coverage. Its distinguishing feature is that it provides “support for large-scale enterprise software development while keeping individual developer’s work fast and iterative.” The toolkit is 100% Java-based, with no external library dependencies, and works in any Java 2 JVM (even 1.2.x).


Embunit is aimed at programmers and testers developing software in C or C++. While it’s primarily designed for embedded software development, it can be used to develop unit tests for any software written in C or C++. The desktop version of Embunit is free, but the enterprise version is priced for cloud-based deployment. It’s designed to be flexible and is customized to create unit tests for almost any hardware platform, even the smallest microcontrollers.


PHPUnit is a programmer-oriented testing framework for PHP, testing small units of code separately. It includes a lot of simple and flexible assertions, enabling easing testing of code. PHPUnit includes a set of application test helpers, allowing developers to write straightforward PHPUnit tests to test complex sections of applications.


This open-source JavaScript testing tool runs on Node.js and in the browser, with features like test coverage report, browser support, and report test duration. Mocha tests run serially, enabling flexible and accurate reporting while mapping uncaught exceptions to the correct unit test cases.


Developed by QA Systems, Cantata is a unit and integration testing tool that allows developers to verify standard-compliant or business-critical code on host native and embedded target platforms. It achieves dynamic testing requirements by automating test framework generation, test execution, and results from diagnostics and report generation. Canata 9.1 extends the testing tool’s AutoTest capability to provide automatic test generation for C++ code and adds HTML-certified test results output.


SimpleTest is a PHP unit test and web test framework, supporting SSL, forms, proxies, and basic authentication. It can easily test common but finicky PHP tasks, such as logging into a site. SimpleTest also includes autorun.php.file to turn test cases into executable test scripts. The developer has a page to help newcomers to the framework get up and running quickly.

Make unit testing your competitive edge

By implementing unit testing, it’s easier to catch and fix issues early before they cost extra time and money. It can become an important part of the overall software development process, helping to foster development more efficiently and productively.

To make unit testing your competitive edge, source the right independent software developer on Upwork who has the skills and experience to handle all the complexities of your next software project.

Upwork is not affiliated with and does not sponsor or endorse any of the tools or services discussed in this section. These tools and services are provided only as potential options, and each reader and company should take the time needed to adequately analyze and determine the tools or services that would best fit their specific needs and situation.

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What Is Unit Testing? Frameworks, Examples, and Best Practices
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