Unit Testing: Definition, Process, Techniques, and More


Unit testing is among the most important types of software testing. It ensures that the various modules (units) of a program are working correctly. It is a kind of functional testing. In this blog, we will know the definition, goals, process, pros, cons, and more of unit testing.

What is Unit Testing? [Definition]

In a unit test, the smallest testable pieces of a program, known as units, are evaluated separately and independently for ensuring expected performance.

Software developers and, on occasion, QA personnel use this testing methodology during the development process. The major goal of running unit tests is to separate written code in order to test and verify if it performs as expected.

Unit testing is an important phase in the software testing life cycle because, when done correctly, it can assist to uncover defects early that are more difficult to find during later stages of the testing process.

Test-driven development (TDD) is a pragmatic methodology that takes a thorough approach to produce a product through continuous testing and revision (improvement). Unit testing is a component of TDD.

This testing approach is also the first level of software testing, and it comes before other types of testing like integration testing and UAT.

Unit tests ensure that a unit (module) works perfectly on its own without relying on any external code or functions. Although you can run unit tests manually, automated testing is the usual norm.

Goals of Unit Testing

A unit test aims to:

  • Isolate a code section.
  • Ensure that the code is correct.
  • Test each function and approach.
  • Fixing issues early in the development cycle, thus, saving money.
  • Assist developers in comprehending the codebase and making changes rapidly.
  • Aid with code reuse.

How do Unit Tests Work? [The Process]

The typical workflow of a unit test is as follows: 1) Create Test Cases 2) Baseline 3) Review/Rework 4) Carry out the test cases. Usually, a unit test comprises three stages:

  1. Planning,
  2. Designing test cases and scripts, and
  3. Run unit tests.

The unit test(s) is (are) prepared and reviewed in the first stage. The intermediate stage is to create test cases and scripts, and the final stage involves running the unit tests and checking the code.

Developers must first write failing unit tests in test-driven development. They then develop code and rework the program till it passes the test. TDD usually results in a codebase that is explicit and predictable.

To guarantee that the code is free of dependencies, each test case is run independently in a separate environment. A testing framework can be used to report any failed tests, and the software developer should create criteria to check each test case.

Developers should not write a test for every line of code because it will take too long. Therefore, developers should then construct tests that focus on code that potentially alter the software’s behavior.

Only those features are tested in unit testing that are critical to the unit’s functioning. This enables developers to make modifications to the source code without worrying about how they will influence the operation of other units or the program as a whole.

Integration testing can be used to analyze larger components of a program once all of the units have been confirmed to be working in the most efficient and error-free manner possible. Unit tests should be run on a regular basis and can be done manually or automatically.

Advantages and Disadvantages of Unit Testing

Unit tests bring the following benefits to the table:

  • Compound errors are less likely to develop if an issue is discovered early.
  • The cost of resolving a problem sooner rather than later can quickly outweigh the cost of resolving it later.
  • The debugging procedure is simplified.
  • Developers can make modifications to the codebase fast.
  • Developers can also migrate code from one project to another.

Like every other great thing, unit testing has its issues. Important drawbacks of running unit test scripts include:

  • Tests will not find every flaw.
  • Unit tests just test data sets and their functionality; they do not catch integration problems.
  • Multiple code lines may be required to test a single line of code. This could result in a significant time.
  • Learning using specialized automated unit test tools might be a challenging task.

How to Get the Best Results with Unit Testing?

A unit test can deliver the best results while avoiding misunderstanding and increasing complexity by leveraging these strategies:

  • Because any change or enhancement to the requirement will not affect the test cases, they must be independent.
  • Unit test case naming guidelines must be simple and consistent.
  • Before moving on to the next phase of the SDLC methodology, the found defects must be rectified during unit testing.
  • Only one code should be tested at any given moment.
  • If you don’t use test cases when writing your code, the number of execution routes will expand.
  • If the code of any module changes, make sure the relevant unit test is provided.

Unit Testing Techniques

Developers write a chunk of code to test a specific function in a software application as part of unit testing. Developers can also isolate this function to test it more thoroughly, revealing any unwanted dependencies between the tested function and other units that can be deleted. There are two ways to perform a unit test:

  1. Manual
  2. Automated

Unit testing is frequently automated, although it can also be done manually. Automation is preferred over manual programming in software engineering. A manual approach to running unit test scripts can employ a step-by-step instructional paper.

In automated testing, a developer creates a chunk of code in the program only for the purpose of testing the function. Once the program is deployed, developers will comment out and eventually eliminate the test code.

A developer could also isolate the function in order to thoroughly test it. This is a more extensive unit testing method that requires copying and pasting code into a separate testing environment from its natural one.

Alienating the code helps find unwanted dependencies between the code under test and other units or data spaces in the product. This reliance can then be removed.

To create automated test cases, most programmers utilize the UnitTest framework. The developer writes criteria into the test using an automated framework to ensure that the code is correct.

While failing test cases are being executed, the framework logs them. Many frameworks will also highlight and notify these failed test cases automatically. Depending on the severity of a failure, the framework may halt further testing.

Approaches of Unit Testing

Black box testing, white box testing, and gray box testing are the three approaches to execute unit test scripts. Black box testing entails testing the user interface as well as input and output.

White box testing involves testing the software application’s functional behavior, and gray box testing involves running test methods, test suites, test cases, and risk analysis. Unit testing methodologies include the following:

  • Coverage of decisions
  • Coverage by branch
  • Statement protection
  • Coverage by condition
  • Coverage of finite state machines

Tools for Unit Testing

Running a unit test script can be made easier with the help of automated unit test tools. These tools come with a galore of features beyond test creation and execution:

  1. NUnit
  2. JUnit
  3. PHPUnit
  4. Parasoft Jtest
  5. EMMA


If you want to design complicated software products, you should master unit testing. Bugs may have a lower possibility of appearing or producing. As a result, developers must write their own unit test scripts for each module and test them before passing them over to the QA team.

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