What is Unit Testing and How does it Work? An Overview and Its Use Cases

History & Origin of Unit Testing

In 1997, a programmer named Kent Beck created a development environment plugin, JUnit, to test small pieces of code. Developers wrote test code that assessed the source code. He called the approach unit testing.

A unit test is a way of testing a unit – the smallest piece of code that can be logically separated into a system. In most programming languages, this is a function, a subroutine, a method, or a property. The separate part of the definition is important. In his book “Working Effectively with Legacy Code”, author Michael Feathers states that such tests are not unit tests when they rely on external systems: “If it talks to a database, it can run across the network.” If it touches the file system, it requires system configuration, or it cannot be run at the same time as any other test.”

What is Unit Testing?

Unit testing is a software testing technique through which individual units of software i.e. groups of computer program modules, usage procedures, and operating procedures are tested to determine whether they are suitable for use or not. It is a testing method using which each independent module is tested to determine if there is a problem by the developer himself. This is correlated with the functional correctness of the independent modules.

Unit testing is defined as a type of software testing where individual components of the software are tested. Unit testing of software products is done during the development of an application. An individual component can be either an individual act or a process. Unit testing is usually done by the developer.

Features of Unit Testing are:

  • Makes the Process Agile
  • Quality of Code
  • Finds Software Bugs Early
  • Facilitates Changes and Simplifies Integration
  • Provides Documentation
  • Debugging Process
  • Design
  • Reduce Costs

Why use Unit Testing

  1. Discipline and Rigor
  2. Does It Work?
  3. Reduce Cyclomatic Complexity
  4. Your Software Is Used Before Delivery
  5. Documentation
  6. Measure the Effort Needed to Modify an Existing Feature
  7. Enforces Inversion of Control/Dependency Injection Patterns
  8. Code Coverage
  9. Performance
  10. Enables Continuous Integration (CI)

Advantages of Unit Testing

  • The process becomes agile. This is the main benefit of unit testing. …
  • Quality of Code. Unit testing significantly improves code quality. …
  • Find Software Bugs Easily. …
  • Facilitates Change. …
  • Provides Documentation. …
  • Debugging Process. …
  • Design. …
  • Reduce Costs.

Disadvantages of a Unit Testing

  • It takes time to write test cases.
  • It’s difficult to write tests for legacy code.
  • Tests require a lot of time for maintenance.
  • It can be challenging to test GUI code.
  • Unit testing can’t catch all errors.

Best Unit Testing Alternative

  • NUnit.
  • JMockit.
  • Emma.
  • Quilt HTTP.
  • HtmlUnit.
  • Embunit.
  • SimpleTest.
  • ABAP Unit.

Best resources to learn Unit Testing



Free Video Tutorials Unit Testing

Unit Testing Interview Questions and Answers

1. What Is Unit Testing?
Unit testing is a validation and verification methodology where the developers test the individual units of source code. Some key points to be remembered from: –

  • A unit is the smallest part of the application which can be tested. So it can be either a method. Function or class.
  • These tests are conducted during development.
  • Unit test belongs to the white box testing category.

2) What Are The Different Ways By Which You Can Do Unit Testing With .net?
There are 2 primary/accepted ways of doing unit testing:-

  • Visual studio team edition test system

3) What is Code Coverage?
Code coverage is a metric that determines the number of lines of code validated successfully by a testing process, which helps to analyze how software is verified in depth. Of course, the ultimate aim of any software company is the development of software products for businesses. But, in order to achieve that goal, companies must ensure that all the essential quality features of the software they develop are accurate, maintainable, effective, trustworthy, and safe.

4) Tell some brief about Unit testing?
A unit test is a way to test a unit, the smallest code in a system that can logically be isolated. This is a function, a subroutine, a procedure, or a property in most programming languages. The single part of the definition is significant. Author Michael Feathers says in his book “Working Effectively with Legacy Code” that tests are not unit tests when relying on external systems: “If you talk to the database, you talk through the network, touch the file system, you need a system configuration, or you cannot run it simultaneously with any other test.”

5) How to check timeout testing, and write some code?
Here is the code from which we can check the timeout testing

@Test (timeout=10)
Public void infinity(){

6) What is Branch Coverage?
Branch coverage is a test method to ensure that all access codes can be executed at least once each of the potential branches is executed from each decision point. In other words, every branch is right and wrong. In addition, it helps validate all the branches in the code to ensure that no branch results in abnormal application behavior.

7) What is the Advantage of unit testing?
There are many advantages of unit testing; some are UT simplifies the debugging process. UT forces better code and design, whether you use C#, Python, Java, JavaScript, or PHP. It means that you have a well-defined and cohesive code. Using unit testing and good unit testing tools, the total cost of a project is reduced. Early detection of bugs means fewer late changes and easier problems than if they were made later.

8) Who can perform Unit Testing?
The developers usually perform unit testing during the development phase. At the same time, unit testing is usually done by automation engineers and QA experts if developers are occupied with other development tasks.

9) How can Unit test cases be avoided?
It can help avoid long classes, procedures, functions, etc. when you are working with unit test cases. No long code is necessary, but the functionality of each small component needs to be tested step by step. It makes it easy to develop big apps.

10) List some various coverage code techniques
Here is the list of coverage code technique

  • Condition coverage
  • Statement coverage
  • Decision coverage
  • Branch Coverage

11) What does the term Refactoring mean?
This technique is used if you want to revamp any existing code. It is usually done in small steps in which the code alteration is not the functionality or logic. It also helps to correct bugs.

12) Tell me about Unit Testing in brief.
Unit Testing is used to check the independent modules of a software app during the development phase. An independent module can be anything like procedure, function, etc. Unit testing is done by developers and testers together before the integration testing. They have to write unit test cases as well if needed.

13) What is the total number of phases in a Unit Test Case?
The working of a unit test case can be divided into 3 phases. In the first stage, it will initialize the specific module of a software app that you want to test. In the second stage, it will execute the test case. In the end, it will analyze the final output.

14) What are the various types of Unit Testing for a software app?

  • State-based Unit Testing
  • Interaction-based Unit Testing

15) What do you know about state-based Unit Testing?
If you want to check if the final output is right or not, then it becomes state-based.

16) Tell me about interaction-based unit testing in brief.
If you want to check the behavior of functions or procedures, whether they are invoked in the right way or not then it is interaction-based.

17) Have you ever used or worked on Unit test frameworks? If yes, name them.
Yes, I do have practical knowledge of unit test frameworks, Junit, and TestNG.

18) Tell me about the Junit testing framework.
Several test cases need to be executed repeatedly. If you need test cases for repeated execution then the Junit framework can help you.

19) Who can perform Unit Testing?
Unit Testing is generally done during
the development phase so that it can be performed by developers. At the same time, if developers are occupied with other development tasks then unit testing is generally performed by automation engineers and QA experts.

20) What do you know about the term Refactoring?
If you want to revamp any existing code, then this technique is used. It is generally done in small steps where only the code is changed, not the functionality of the logic. It helps in bug fixing too.