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What is Unit Testing? Unit Testing Tutorial Guide for Beginners

Unit Testing is an essential instrument in the toolbox of serious software developers. However, it may be difficult sometimes writing a good unit case of a particular piece of code. The reasons may vary for different developers. For example, lack of fundamental testing knowledge, developers are not aware of secret testing techniques, best practices for unit testing, tips for writing maintainable unit cases or more.

In this blog, we will address all the possible issues and tips on writing testable unit cases that are highly valuable for developers. The objective of a developer is not writing testable code but making it more robust and easier to maintain.

A list of topics to be covered in the blog include:

  • What is Unit Testing?
  • Unit Test vs. Integration Test
  • What Makes a Good Unit Test?
  • Why Unit Testing?
  • How to do Unit Testing
  • Unit Testing Techniques
  • Unit Testing Tools
  • Test Driven Development (TDD) & Unit Testing
  • Unit Testing Myth
  • Unit Testing Advantage
  • Unit Testing Disadvantages
  • Unit Testing Best Practices

What is Unit Testing?

Unit Testing is a software testing technique for instantiating a small portion of an application and verifies the behavior of each part independently. Unit Testing is performed during the application development phase. A unit may be anything like procedure, function, etc. The unit testing is performed usually by developers. In V-model, SDLC, STLC, unit testing is the first phase of testing before integration testing. It is a white box testing technique and QA engineers can also perform Unit Testing if required.

A typical unit test case consists of three phases:

  • First, it initializes the small piece of an application that you want to test.
  • In the second step, it applies a stimulus to the system under test by calling a method.
  • In the final step, it observes the resulting behavior.

If the observed behavior matches the expectations of the client, then the unit test passes. This step process is also named as the AAA, i.e. Arrange, Act, and Assert.

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

A unit test falls into one of two categories either state-based or interaction-based. If you verify that resulting state is correct or not then it is called as state-based unit testing. If you verify that certain methods are invoked properly or not, it is called the interaction-based unit testing. Users are often confused between unit testing and integration testing. Let us understand the difference between the two before we discuss the unit testing in depth.

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Read: Unit Testing Interview Questions and Answers

Unit Test vs. Integration Test

Once you are sure of Unit Testing, another important thing to consider here is the difference between unit testing and integration testing. The purpose of unit testing is checking the behavior of each part of a software that is independent of other parts. Unit tests are narrower in scope, allow us to cover all cases and ensure that every single part works perfectly. It is quite easy to implement and isolated from other parts of an application.

On the other hand, integration testing verifies that different parts of a system work fine together in the real-life environment. It is the high-level testing that validates complex scenarios. It usually demands external resources like web servers, databases to be available. The integration testing covers the interactions between different components close to the real-life environment and requires more efforts to complete.

When unit testing and integration testing are combined for an application, it makes sure that every single unit works perfectly and when all these units integrated, they play nicely. It gives a high level of confidence that the whole system works as expected. However, we should always remember what kind of test we are implementing either it is a unit test or integration test.

However, the difference may sometimes be deceiving because there are cases when unit tests demand external resources like web servers or database to be present. When it happens, something is not right, and we need to crack the issue here. In most cases, the reason is bad Unit test design. So, what makes a good unit test to avoid these types of issues? In the next section, we will focus on the same or best practices for making a good unit test.

What Makes a Good Unit Test?

In this section, we will discuss the properties of a good unit test or principles followed by a good unit test.

Easy to code

It is easy to code unit tests to check different aspects of an application without putting much time or efforts by developers.

More Reliable, Readable, and Faster

  • Unit tests don’t fail even if there is a bug in the system under test. Good unit tests will not be affected by external factors like environment or running order. If it happens, then it is definitely a design flaw.
  • Moving ahead, a good unit test is clear and tells the story about the behavior aspect of an application. It is easy to understand through test cases which scenario has been tested. If the test fails then addressing issues is a pleasing experience. With a good unit case, we can fix bugs much faster without debugging the code.
  • The unit tests are written in such a way that they can be used repeatedly and no bugs are introduced. Adding slow unit tests means stuck waiting a while. Slow unit tests mean system under test interacts with external systems and making it environment – dependent.

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Truly unit, not integration

Unit tests and integration tests are designed for different purposes. Both unit tests and system under test should not access the network resources, file systems, or databases, etc. to eliminate the overall influence of external factor that makes it truly unit, not integration testing.

Read: Automation Testing Tutorial Guide for Beginner

That’s all. There are no secrets in writing unit tests, but they are easy to code and maintain. We can say these are a few techniques to make the code more testable and maintainable.

What is the need for Unit Testing?

Sometimes, developers skip out unit testing due to lack of time, but it is not true, it is just a myth. Skipping out unit testing leads to more defects fixing costs during integration, Beta, and system testing. Proper unit testing at the time application development saves time and money. Here are the key reasons to perform Unit Testing.

  • The defects can be fixed early at the development stage, and it saves time and costs both.
  • It helps developers to understand the code base and make changes quickly that you think of.
  • Good unit tests generally serve as the project documentation.
  • Unit tests can be reused and migrated to the new project quickly when required. You should tweak the code a bit to run again.

How to perform Unit Testing?

Unit testing is divided into major categories, manual and automated. It is good practice automating unit tests, but it can be performed manually as well. It is tough using one over the another, but automated unit testing is a preferable choice here. A manual approach employs a step-by-step instruction document. Here are the steps for the automated approach under Unit Testing.

  • A developer writes the unit tests to check the functionality of a particular piece of application. They are comment out and removed later once the application is deployed successfully.
  • The function should be isolated to test it more rigorously. It is the best unit testing practice to copy and paste the code in the testing environment instead of the natural environment. The isolated code helps to reveal and eliminate the dependencies between the tested code and the data spaces.
  • There is a unit test framework for developing automated test cases. This automation framework helps to write the code and verifies either code is written correctly or not. During the execution of unit tests, the framework logs the status of test cases. Based on the severity of failures, the framework may halt subsequent testing.
  • The unit test workflow is divided into four categories; these are creating test cases, review, baseline, and execution of test cases.

What is Unit Testing Techniques?

The code coverage techniques in unit testing can be given as below. What is Unit Testing Techniques? The unit testing technique is software engineering are given as below.

  • White Box Testing – With the help of a User Interface, input and output are tested.
  • Black Box Testing – It helps to test the behavior of different functions used within an application.
  • Grey Box Testing – It is used to execute tests, risks, and assessment methods.

Unit Testing Tools

There are a plethora of automated tools available to assist with unit testing. Here we have given examples of the most popular ones for your reference. Unit Testing Tools

  • Jtest: It is an IDE plugin that leverages open source frameworks with guided and easy one-click actions to create, scale and maintain unit tests. Once you automate these time-consuming aspects of the unit testing, it allows developers to focus more on the business logic and create more powerful test suites.
  • Junit: It is a free testing tool based on the Java Programming language. It provides assertions to identify different test methods. This tool tests the data first before inserting it to the piece of code.
  • NUnit: it is a widely used testing framework based on the dot programming languages. It is an open source allows writing scripts manually. It supports the data-driven tests to run in parallel.
  • JMockit: it is again an open source testing tool and a code coverage tool with path and line metrics. It allows mocking API with verification and recording syntaxes. The tool offers maximum path coverage, line coverage, and data coverage.
  • EMMA: it is an open source toolkit to analyze and report code written in the Java language. It supports code coverage like methods, line, and basic blocks. This tool is Java-based and able to access the code without any external library.
  • PHPUnit: it is a popular testing tool for PHP programmers. It uses a small portion of code called units to test each of them separately. The tool allows developers using pre-defined assertion methods to make sure that system behaves in a certain manner.

These are just a few unit testing tools highly popular in the technology marketplace. There are lots more, and you are free to choose any of them based on your needs and requirements. To check the list of top 15 penetrating testing tools in 2019, click here.

Unit testing in Test-Driven Development (TDD)

Unit testing in test-driven development involves the extensive use of testing frameworks. A testing framework is generally required for creating unit test frameworks that are not unique to TDD, but they are essential to it. Here are some facts what TDD brings to the world of unit testing.

  • Unit tests are often written before the code.
  • It heavily relies on testing frameworks to write or automate unit tests.
  • It is used to test all classes within an application.
  • It allows easy and quick integration when required.

Unit Test Myth

There is a common Myth that Unit testing takes time and I am already overscheduled. I don’t require unit tests as my code is rocking! These are just false assumptions and leads to a vicious cycle as follows: Unit Test Myth The truth is that unit testing increases the overall development speed. A few developers think integration tests will catch errors and there is no need for unit testing. But this is not true. Bugs in case of unit testing are quickly found and fixed as soon as they are traced.

Read: Sanity Testing Tutorial Guide for Beginner

Unit Testing Advantages

  • Unit testing makes it easy changing and maintaining the code. When good unit tests are written, they can identify issues; every time code is run or changed. If the code is less interdependent, the intended impact is also less.
  • Codes can be reused with unit testing. It should be more modular that means easy to reuse when required.
  • The development is faster with unit testing. If the unit testing is in place, write the code and run the test without setting any breakpoints. It may take time in writing unit tests, but running tests is usually simpler. You just have to fire up the GUI and provide the all necessary inputs.
  • Unit tests are more reliable and run faster in the long run. The efforts taken to write and fix defects during unit testing are very less when compared to efforts required to fix bugs during system testing or acceptance testing.
  • The cost of fixing a defect in unit testing is lesser when compared to that of defects detected at higher levels. For example, consider the costs of acceptance testing or when the software is live.
  • Unit testing makes debugging easy. When a test fails, the latest changes needs to be debugged again. Testing at higher levels will scan changes made over several days, weeks, months, etc.
  • It improves the design of code and allows code refactoring. Even at the later code, it makes sure that the module is still working correctly. The process is writing test cases for methods or functions, so whenever changes cause a fault, it can be identified or fixed quickly when needed.
  • Unit tests when integrated gives the build equality as well.
  • Developers can understand what functionality is performed by a particular unit and look at unit tests to gain a basic understanding of API.
  • As unit tests are modular, it is possible testing selected part of the code without waiting other to complete.

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Unit Testing Disadvantages

  • Unit testing is not expected to catch every error in the program.
  • It is not able to evaluate all execution paths even in the case of trivial programs.
  • It majorly focuses on units and not able to catch integration errors at the broader level.

This is the reason that unit testing should be performed in conjunction with other testing activities to produce more accurate results.

Unit Testing Best Practices

  • Each unit should be independent. In case of any advancements or changes, other units should not be get affected.
  • It is used to test only one code at one time.
  • You should always use clear and consistent naming conventions for unit tests.
  • For each unit, there should be a separate test case before it is passed for implementation.
  • Bugs should be fixed in advance before proceeding with the next phase in SDLC.
  • The more code you write, the more path you have to check for errors.

Final Words:

This is clear from the discussion that there is a lot of things involved in unit testing. IT can be simple or complex based on the nature of an application being tested and tools or strategies used for the testing. Only one thing is certain here that unit testing is always required at some level to make an application more robust and functional as compared to non-tested applications.

The other common types of testing in software engineering involve Regressing Testing, User Acceptance Testing (UAT), End to End Testing, and more. You can go through online blogs, free tutorials to learn different type of testing or you can join QA certification program at JanBask Training to start a successful career in the testing domain and learn all testing concepts from basic to advance thoroughly.


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    JanBask Training is a leading Global Online Training Provider through Live Sessions. The Live classes provide a blended approach of hands on experience along with theoretical knowledge which is driven by certified professionals.


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