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Differences between Black Box Testing and White Box Testing

By Tom Collins, Community Contributor -

Software testing is a mandatory part of its development process, and it is essential to produce standard quality software. The testing identifies bugs, removes them, and improves the overall quality of your software. The procedure follows some common techniques to test your software. Black box testing and white box testing among the types of testing that widely used.

  • Black box testing checks the accuracy of your system without too much concern about the internal implementations. It identifies the interface-level bugs and resolves them.
  • White box testing deeply scrutinizes and analyzes your system by checking its internal coding. So, it helps you to find bugs from the design level, re-construct, run and execute them. In this way, it eliminates the bugs from your system.

What is Black Box Testing?

Black box testing checks whether your system is working according to the business requirement and end-users’ expectations without considering its programming or the internal functionalities. By conducting this testing, the testers enter the UI level inputs and check whether the produced output meets the actual requirement.

As they don’t have access to the source code, they conduct this test on the interface of an application.

Characteristics of Black Box Testing

  • The QAs can perform this test without knowing the logical structure of your application. Thus they don’t require an understanding the algorithm for the system. They just check the external functionalities and behavior of the app. Thus they can test the software independently without involvement in the development procedure.
  • It includes a requirement-specific approach for the testing. So you need to enter the specific input for a particular field of your app’s interface to obtain the successful test results. 
  • As you know, it doesn’t require too much coding knowledge; it’s conducted through the view of an end-user to ensure the app satisfies their expectations and requirements. Also, it confirms the app is easy to handle from the client side.
  • You can perform different types of black box testing, such as functional, non-functional, and regression testing.
  • You can modify the scalability of this testing depending on the size and complexity of your application.

Testing Perspective and Focus

You have to execute this testing from the end-user perspective and focus. Thus, you must check the app’s behavior, basic functionalities, usability, compatibility, etc. Mainly, it focuses on usability and common functionality. But you don’t need any prior understanding of the application. Simply, you must provide the specific functionality input and examine the output.

Test Case Design

First, you need to understand the specific requirement for this testing. You will get the requirement from the SRS (Software Requirement Specification) documents. Then you have to determine different sets of valid inputs and test scenarios. Based on them, you can create your test cases.

A common example is your application login page. Here you can make the following test cases

  • Case 1: If you enter the correct username and password, you will easily log in to the application.
  • Case 2: You will get the’ incorrect password’ prompt if you enter the correct username and wrong password.
  • Case 3: When you enter the correct password but the wrong username, you see the ‘incorrect username’ prompt.
  • Case 4: You will find the ‘incorrect username and password’ prompt when you enter the incorrect username and password.

Testers’ Knowledge and Access to Internal Code Details

Black box testing doesn’t require typical programming knowledge. You don’t need to know complex algorithms, structures, or instructions. They don’t even need to understand the server logic. Usually, this testing is done by testers who need more coding knowledge. They need to enter the specific inputs and check the outcomes. If there is any error, the development team will fix the issue.

Advantages and Limitations of Black Box Testing

The advantages of this Black Box testing are

  1. You don’t need to learn any programming language to test the black box. But you have to understand the users’ requirements and expectations. 
  2. The testers don’t wait for the entire development process to complete because black box testing is independent of the development. Thus you can create your test cases before starting the development.
  3. This testing technique has a similarity with the agile methodology.
  4. The test cases are reusable. That means you can use the test cases for future testing purposes.

The limitations of Black Box Testing are

  1. There needs to be more granularity in this testing because the testers need to learn the internal working process of the system. Thus there are huge chances of missing minor errors.
  2. The testing process is slow and time-consuming. Thus it’s not suitable for large and complex systems. 

Scenarios Suitable For Black Box Testing

 You can create two types of test scenarios – positive test scenarios and negative test scenarios. You must deliver valid input to the system for the positive scenarios and vice versa for the negative ones.

For example, a system supports the number from 0 to 99 for boundary value analysis. If you enter any number within this range, that will be your positive scenario. But when you enter 100 or -1, which will be your negative scenario.

What is White Box Testing?

White box testing checks the internal procedure of your system, including coding, structure, logic, and architecture. Thus, the tester must have in-depth coding knowledge to handle the testing technique. Generally, the developers perform this technique. When performing this testing, they have complete access to the system’s source code.

Characteristics of White Box Testing

Here are the characteristics of the white box testing

  • White box testing is directly dependent on the software development process. So, you can write the test cases without starting the development process.
  • It requires programming language knowledge to understand the app’s structure and design. You have to test every function and module of the application.
  • This testing technique helps to check the code coverage. That means it can identify the areas of your application that are not tested enough or skipped. 
  • It identifies logical errors like – infinite loops, coding threads, incorrect conditions, etc. Then it commands to rectify them and improve the functionality of the coding structure.

Testing Perspective and Focus

You have to perform this testing from a developer’s perspective. So, you need an advanced knowledge of programming language because it requires understanding the workflow of the source code. Then you must focus on every statement, including the conditional statement (statement coverage), expected outputs, and execution paths (path coverage). 

If you find any error in the code, you have to modify them, run, debug, and execute them to fix the issue. By testing the software’s internal structure, WBT ensures that the software functions as expected and meets the required standards.

WBT practices are crucial to the SDLC, contributing to developing high-quality, secure, and efficient software.

Test Case Design Based On Specifications and Requirements

A test case of white box testing covers coding-specific requirements. For example, 

  • You have to check that 3+3 equals 6 for an additional operation. This will be your statement coverage testing.
  • You must test that 3/ 0 gives an error message for path coverage testing. This statement needs an infinite path coverage. Thus it will show the error.

Testers’ Knowledge and Access to Internal Code Details

Already we have discussed that you need a clear understanding of coding to conduct this testing. So, you need to analyze the source code through its overall working procedure. It includes testing every statement, loop, nested loop, branch, and path. 

Advantages and Limitations of White Box Testing

This technique has the following advantages

  1. It provides thorough testing of the entire code. So, it improves the granularity of your testing.
  2. It optimizes your code by reducing errors, unnecessary coding lines, and data redundancy. So you can easily maintain the standard of coding through it.
  3. You can start this testing at the early stages of SDLC. Unit and integration testing are the types of this testing technique.
  4. You can easily automate this testing using test automation tools like- SeleniumAppium, TestNG, etc. Thus it’s a time-saving technique.

There are a few limitations of this testing. They are – 

  1. It’s a complex testing technique because you must understand the internal working process. So, for a large system, it creates more complexity.
  2. There is no chance to reuse the test cases. Every time you should rewrite the test cases and redesign the code.

Scenarios Suitable For White Box Testing

You have to perform white box testing in the following scenarios –

  • If you want to test the working process of your application, then you should test the methods, modules, and classes of your coding. In this case, you need the white box testing.
  • When you find an incorrect statement or broken path within the coding, you should find out the errors and fix them. This testing technique also conducts it.

Differences between Black Box Testing and White Box Testing

Black Box TestingWhite Box Testing
Testing perspective and focusYou have to perform this testing from the users’ aspect. So, your focus should be on the app’s usability, performance, and user interface. You need to focus on the internal coding of the software. It includes the statement, methods, loops, and security loopholes also. Thus you need a developer mindset to perform this testing.
Knowledge of internal code detailsIt considers the external behavior of software. So you don’t need any coding knowledge in this case.But it checks the internal functionality of software. So you need to grab the coding knowledge for this.
Testing approachIt follows the data-driven approach. So, it includes methods like boundary value analysis, equivalence partitioning, error guessing, etc.It follows the code coverage approach. So, it includes methods like statement coverage, branch coverage, path coverage, etc.
Test coverageIt lacks test coverage because it can’t find out the small defects of your application. So, it can’t cover all the test cases.It improves the test case coverage by checking your code line-by-line and discovering small defects.
Test case independence  The test cases are independent of the development procedure. You can start writing the test cases before the development.It completely depends upon the development process. So, you have to create the test cases after starting the procedure (at the early stages of development)
Skill requirementsYou need a user-level understanding of an application. No coding knowledge is needed. You must understand the coding of the app. So, you need pure technical skills to handle this testing.

Selecting the Appropriate Testing Approach

Black box testing considers the behavioral testing strategy and white box testing follows the structural testing strategy. 

  • For the behavioral approach, you need proper planning, test case design, execution, and result checking. It checks the system’s behavior through the view of users. You need to perform manual testing to follow this approach.
  • The structural approach checks the implementation of each module of software. After writing the tests, you must commit the test cases in the source code repository. Automation testing is the best-fitted technique for this.

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