What is Unit Testing?

Unit Testing
Unit Testing

What is Unit Testing?

Unit Testing

In computer programming, unit testing is a procedure used to validate those individual units of source code are working properly.

A unit is the smallest testable part of an application. In procedural programming, a unit may be an individual program, function, procedure, etc., while in object-oriented programming, the smallest unit is a method, which may belong to a base/ super class, abstract class or derived/ child class.

Ideally, each test case is independent of the others; mock or fake objects, as well as test harnesses, can be used to assist testing a module in isolation. Unit testing is typically done by the developers and not by software testers or end-users.

Benefits of Unit Testing

The goal of unit testing is to isolate each part of the program and show that the individual parts are correct. A unit test provides a strict, written contract that the piece of code must satisfy. As a result, it affords several benefits.

Facilitates change

Unit testing allows the programmer to refactor code at a later date, and make sure the module still works correctly (i. e. regression testing). The procedure is to write test cases for all functions and methods so that whenever a change causes a fault, it can be quickly identified and fixed.

Readily available unit tests make it easy for the programmer to check whether a piece of code is still working properly. Good unit test design produces test cases that cover all paths
through the unit with attention paid to loop conditions.

In continuous unit testing environments, through the inherent practice of sustained maintenance, unit tests will continue to accurately reflect the intended use of the executable and code in the face of any change.

Depending upon established development practices and unit test coverage, up – to – the – the second accuracy can be maintained.

Simplifies integration

Unit testing helps to eliminate uncertainty in the units themselves and can be used in the bottom-up testing style approach. By testing the parts of a program first and then testing the sum of its parts, integration testing becomes much easier.

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A heavily debated matter exists in assessing the need to perform manual integration testing. While an elaborate hierarchy of unit tests may seem to have achieved integration testing, this presents a false sense of confidence since integration testing evaluates many other objectives that can only be proven through the human factor.

Some argue that given a sufficient variety of test automation systems, integration testing by a human test group is unnecessary. Realistically the actual need will ultimately depend upon the characteristics of the product being developed and its intended uses. Additionally, human or manual testing will greatly depend on the availability of resources in the organization.


Unit testing provides a sort of living documentation of the system. Developers looking to learn what functionality is provided by a unit and how to use it can look at the basic understanding of the unit API.

Unit test cases embody characteristics that are critical to the success of the unit. These characteristics can indicate appropriate/ inappropriate use of a unit as well as negative behaviors that are to be trapped by the unit.

A unit test case, in and of itself, documents these critical characteristics, although many software development environments do not rely solely upon code to document the product in development.

On the other hand, ordinary narrative documentation is more susceptible to drifting from the implementation of the program and will thus become outdated (e. g. design creep, feature creep, relaxed practices to keep documents up to date).

Unit Testing techniques

  • Unit testing is commonly automated, but may still be performed manually. The IEEE does not favor one over the other. A manual approach to unit testing may employ a step – by – step instructional document. Nevertheless, the objective of unit testing is to isolate a unit and validate its correctness.
  • Automation is efficient for achieving this and enables the many benefits listed in
    this article. Conversely, if not planned carefully, a careless manual unit test case may execute as an integration test case that involves many software components, and thus preclude the achievement of most if not all of the goals established for unit testing.
  • Under the automated approach, to fully realize the effect of isolation, the unit or code
    body subjected to the unit test is executed within a framework outside of its natural environment, that is, outside of the product or calling context for which it was originally created.
  • Testing in an isolated manner has the benefit of revealing unnecessary dependencies between the code being tested and other units or data spaces in the product. These dependencies can then be eliminated.
  • Using an automation framework, the developer codes criteria into the test to verify the correctness of the unit. During the execution of the test cases, the framework logs those that fail any criterion. Many frameworks will also automatically flag and report in a summary these failed test cases. Depending upon the severity of a failure, the framework may halt subsequent testing.
  • As a consequence, unit testing is traditionally a motivator for programmers to create decoupled and cohesive code bodies. This practice promotes healthy habits in software development. Design patterns, unit testing, and refactoring often work together so that the most ideal solution may emerge.
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Unit testing frameworks

Unit testing frameworks, which help simplify the process of unit testing, have been developed for a wide variety of languages. It is generally possible to perform unit testing without the support of a specific framework by writing client code that exercises the units under test and uses assertion, exception, or early exit mechanisms to signal failure.

This approach is valuable in that there is a nonnegligible barrier to the adoption of unit testing. However, it is also limited in that many advanced features of a proper framework are missing or must be hand-coded.

Extreme Programming(XP) a hatchery of Unit tests

Unit testing is the cornerstone of Extreme Programming (XP), which relies on an automated unit testing framework. This automated unit testing framework can be either a third
party, e. g. xUnit, or created within the development group.

Extreme Programming uses the creation of unit tests for test-driven development(TDD). The developer writes a unit test that exposes either a software requirement or a defect. This test will fail because either the requirement isn’t ‘ t implemented yet, or because it intentionally exposes a defect in the existing code.

Then, the developer writes the simplest code to make the test, along with other tests, pass.

All classes in the system are unit tested. Developers release unit testing code to the code repository in conjunction with the code it tests. XP’s s thorough unit testing allows the benefits mentioned above, such as simpler and more confident code development and refactoring, simplified code integration, accurate documentation, and more modular designs.

These unit tests are also constantly run as a form of regression test.

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Limitations of unit testing

Testing, in general, cannot be expected to catch every error in the program. The same is true for unit testing. By definition, it only tests the functionality of the units themselves. Therefore, it may not catch integration errors, performance problems, or other system-wide issues. Unit testing is more effective if it is used in conjunction with other software testing activities.

Like all forms of software testing, unit tests can only show the presence of errors; It can not show the absence of errors.

Software testing is a combinatorial problem. For example, every boolean decision statement requires at least two tests: one with an outcome of ” true ” and one with an outcome ” false “. As a result, for every line of code written, programmers often need 3 to 5 lines of the test code.

To obtain the intended benefits from unit testing, a rigorous sense of discipline is needed throughout the software development process. It is essential to keep careful records, not only of the tests that have been performed but also of all changes that have been made to the source code of this or any other unit in the software.

The use of a version control system is essential. If a later version of the unit fails a particular test that it had previously passed, the version – control software can provide a list of the source code changes (if any) that have been applied to the unit since that time.

It is also essential to implement a sustainable process for ensuring that test case failures are reviewed daily and addressed immediately. If such a process is not implemented and ingrained into the team’s workflow, the application will evolve out of the sync with the unit test suite increasing false positives and reducing the effectiveness of the test suite.

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