What is White Box Testing

White box testing is a way to check how the software works by looking inside the code logic. It helps find bugs early by testing things like logic, loops, and conditions. To do this testing, you need to understand the code well. This testing makes the software more reliable and easier to fix before it reaches users. It is useful for developers to ensure each part of the program works as expected.

In this article, you will learn what white box testing is in detail with the help of an example.

Table of Contents: 

• What is White Box Testing?
• Types of White Box Testing
• White Box Testing Techniques
• What Does White Box Testing Focus On?
• Process of White Box Testing
• Features of White Box Testing
• Tools Used for White Box Testing
• Advantages of White Box Testing
• Disadvantages of White Box Testing
• Best Practices for Black Box Testing
• Real-World Applications of White Box Testing
• Black Box vs White Box vs Gray Box Testing
• Conclusion

What is White Box Testing?

White Box Testing is a type of software testing in which the internal structure, design, and code of the software are tested. It looks inside the code to see how the code is working.

It is also known as clear box testing, glass box testing, transparent box testing, and structural testing.

For example, if you are testing a car in white box testing, you will see the internal implementation, i.e., the engine, wires, and internal mechanics of the car, to make sure that everything is working properly. 

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Types of White Box Testing

There are mainly 3 types of white box testing. These are:

1. Unit Testing

In this type of testing, the individual units of the code are tested alone, like a single method or a function. It is usually done by the developers to make sure that each piece of the code works correctly. This testing finds errors in the code easily and is fast and automated.

For example, you have a method add(), now in this method, you will check for the different values to see if it is giving correct or incorrect results. If it is giving an incorrect result, you will check why it is giving the unexpected result.

2. Integration Testing

In this type of testing, multiple units or modules are tested together, to see how they work as a one integrated unit. It is done by the developers or testers after the unit testing is done. This testing finds the bugs when the different components or modules interact with each other. 

For example, you test the login and registration of an application. In this, the coding and the database of both modules will be tested.

3. Regression Testing

In this type of testing, the software is tested after the changes are made in the code, like errors or adding new features. It is done by the testers or the automation systems, and sometimes also by the developers who are present in the agile team.

The main aim of the regression testing is after the changes are made in the software, the main or old functionality of the code does not change. 

For example, you added a new payment method in an application, then you have to re-run the tests or the entire application to check that no errors occur after updating the application.

Note: Regression testing can be both white box and black box, depending on the level at which tests are written.

White Box Testing Techniques

White Box Testing uses the following techniques to test every part of the application, so that every small mistake in the code gets checked. These are some of the methods:

1. Statement Coverage

Statement Coverage ensures that every statement in the program is executed at least once, even if it is the simplest or basic statement. It is the basic form of white box testing. It ensures that no line of code is left untested.

As in the above flowchart, we can see that there are 2 possible statement coverages, i.e., via ACG and via ABDG.

2. Branch Coverage

Branch Coverage ensures that all conditional statements, like if-else, are evaluated for both true and false outcomes. Its main objective is to test that every possible decision is tested at least once. It also ensures the decision logic of the statement. 

In complex cases, it increases the number of required test cases.

In the above flowchart, you can see that there are mainly 4 branches of coverage. They are ACG, ABG, ABDEG, and ABDEFG.

3. Condition Coverage

In this technique, every Boolean sub-condition of the code is tested. It ensures that each condition inside a decision block is tested for true and false.

For example, 

if (A && B) {
    // do something
}

In the above condition,

A = true, B = true

A = false, B = true

A = true, B = false

A = false, B = false

The if block will only be executed when both conditions are true; hence, we have to test all the variations of A and B independently.

4. Path Coverage

In this technique, all possible paths in the code, including different combinations of branches, are checked to catch complex bugs that are present in the code by testing every possible flow.

public void process(int x) {
    if (x > 0) {
        if (x % 2 == 0) {
            System.out.println("Positive Even");
        } else {
            System.out.println("Positive Odd");
        }
    } else {
        System.out.println("Non-Positive");
    }
}

In the above example, the possible paths of the code can be, 

• x > 0, x % 2 == 0, Positive Even
• x > 0, x % 2 != 0, Positive Odd
• x <= 0, Non-Positive

Hence, you need at least 3 test cases to cover all paths. 

5. Loop Testing

Loops are the basic fundamentals of coding problems and are used in almost every functionality of the software. The loops can be simple, nested, and concatenated, according to which the loop testing is conducted as follows:

For Simple Loops

For a loop that runs n times, test it with:

• Test with a value that makes the loop condition false from the start.
• Test with a value that allows the loop to run exactly once.
• Test the loop with one less than its normal maximum.
• Test with a value less than the full loop count.
• Test the loop with one more than expected.

for(int i=0;i<n;i++)
{
      //code
}

For example, if the value of n is 5, then according to the above test cases, the loop will

• Not run if n is 0
• Run once if n is 1
• Run 4 (n-1) times if n is 4
• Run m times, such that m<n (m is 3) 
• Handle logic errors, if m is 6 (m>n).

This will help to find bugs when loops run too few or too many times.

For Nested Loops

for(int i=0;i<n;i++)
{
     for(int j=0;j<m;j++)
     {
           //code 
     }
}

These are loops inside other loops. To test them:

• Start with the innermost loop
• Test it like a simple loop
• Then test the outer loops one by one

This technique catches issues in deeply repeated code.

For Concatenated Loops

These are loops that are placed one after another.

• If the loops are independent, test each one like a simple loop
• If the loops are dependent, test them like nested loops

This ensures each loop works properly, whether alone or connected.

What Does White Box Testing Focus On?

1. Control Flow: It checks condition statements, loops, nested structures, etc.

2. Code Coverage: One of the most important focuses of White Box Testing is to maximize code coverage. It ensures that no part  of the code is left untested

3. Logic and Decision Testing: White Box Testing validates the logical decisions in the code. Its main aim is to find the logical errors that cannot be caught during the Black Box Testing.

4. Internal Functionality and Algorithms: It verifies the correctness of an algorithm, its boundary conditions, performance, and edge cases. Its main purpose is to test the internal processing of the program.

5. Data Flow: It also sees how the data is handled inside the code, like variable initialization, variable scope, and so on. 

6. Error Handling and Exception Flow: It checks how the code handles errors and unexpected events. Its main aim is to ensure the robustness and reliability of the software.

Process of White Box Testing

Now, let us discuss how the white box process is initiated and gets all the testing done.

1. Input

This is the first step of the process of White Box Testing. It starts with gathering all the requirements and the related documents.

• Requirements: This tells what the software has to do for an input and its expected output.
• Functional Specifications: This shows how the software has to perform under the different conditions as per the user’s requirements.
• Source Code: This is the code that has been written by the developer on the basis of the requirements that the user gave. In this, the main functionality and the logic of the code are written.

2. Processing

After the input is given, the next step is the processing.

• Risk Analysis: In this step, the main risk in the code is identified by keeping the functionality of the software in mind. The testers see the areas in which the errors can occur, and the main focus remains on these areas only. 
• Test Planning: In this step, the testers make the test cases for the software that cover all its conditions, like loops, functions, and requirements.  

3. Test Execution

As the test cases are made for the applications in the above cases, in this step, they are checked.

• Execute the tests: The test cases that were made on the above cases are checked. Also, during the execution of these test cases, the main logic of the application is also checked. 
• Error identification and fixing: If the errors are found in the above step, they are reported to the development team to fix them. After which, the development team fixes the errors, and then the test cases are run again for verification of the software. This step is continued until the main errors are solved in the application.

4. Output

When the testing is done, by fixing all the errors in the software, then the final step is performed.

Final Report: In this step, a detailed report of the software is made, which includes all the test cases, errors, and the updated code. This report gives a full overview of all the test cases and the software functionality. The process of white Box testing. This process is repeated if the above steps find bugs in the software.

Features of White Box Testing

The following are the common features of the White Box Testing.

1. Requires Knowledge of Source Code: Code is tested from the inside, i.e., you should first have knowledge of the code to test it. For example, testing an if condition.

2. Checks Logic Flow and Decision Making: It checks the logic flow to test how the program makes the decisions. For example, if age>18, then the user is allowed to vote.

3. Covers All Branches and Paths in Code: It tests all the branches of the code, like if-else statements, loops, and so on.

4. Can Begin Before UI Development: This type of testing can be started before the UI or frontend of the website is made.

5. Used in Unit Testing: It is used in unit testing to test the individual function of the software.

6. Helps Uncover Hidden Bugs: It helps to find the bugs that the real-world user is unable to see.

7. Supports Automation with Tools Like JUnit: You can use tools like JUnit to write test scripts that can be automated.

Tools Used for White Box Testing

Many tools are used for the white box testing; Some of the popular tools are discussed below:

1. JUnit: It is used to write and run unit tests in Java.

2. NUnit: It is similar to JUnit, but is used for C#

3. PyTest: It is a popular Python Testing framework.

4. CppUnit: It is a tool used for testing the C++ language.

5. JaCoCo: Java Code Coverage is a tool that checks which part of the code is tested, and is used for Java.

6. SonarQube: It analyzes the quality of the code and test coverage. It detects untested code and bugs in Java, C#, and other languages.

Now, let us discuss the advantages and disadvantages of the white box testing.

Advantages of White Box Testing

1.  It looks inside the code and makes sure that every line, condition, and loop is tested.

2. As this type of testing is done at the early stages of the development, the errors can be found and fixed before the software is released, which saves time and cost later in the project.

3.  It helps identify the unnecessary lines of code or parts that will never run, which can be removed, making the code more efficient.

4. You can use tools like JUnit, PyTest, or NUnit to write white box tests once and then run them automatically whenever the code has any changes.

Disadvantages of White Box Testing

1. The person who is doing the testing should have good coding knowledge, as a person without knowledge will not be able to perform testing.

2. Testing all possible code paths in large or complex programs can be time-consuming and requires too much effort to maintain.

3. It focuses only on the code of the program; Hence, it will not check how the application looks to the users.

4. If the internal structure of the code changes, many existing tests may stop working and need to be updated again.

Best Practices for White Box Testing

There are many common mistakes that users make. Below are some best practices that the users should follow to avoid common mistakes while performing white box testing.

1. Before starting the testing, make a list of the requirements, or specifications, carefully.

2. Write test cases that cover all types of inputs, i.e., correct inputs that the software should accept, wrong inputs to see how the software handles errors, and boundary input values at the edges, like minimum and maximum.  

3. Before using test cases, check your test cases on your own, which will help find problems that some of the test cases may not be able to find. 

4. Many bugs happen at the limits of input ranges, so carefully check for the edges.

5. Use automation tools to save time and avoid mistakes.

Real-World Applications of White Box Testing

1. White box testing is used where there is a need for unit testing for individual functions or methods.

2. It is used when checking for security flaws in the code, like SQL injection, buffer overflows, or incorrect access control.

3. White box testing helps applications that have a lot of business rules or calculations to ensure every condition is tested.

4. White box testing is important in critical systems like healthcare, aviation, or finance, where small bugs can cause big issues.

5. In modern development (DevOps), white box tests are run automatically whenever the code changes to catch bugs early.

Black Box vs White Box vs Gray Box Testing

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Conclusion

White box testing means checking the code from the inside to make sure everything works the right way. It helps find mistakes early and makes the software better and faster. You need to know some coding to do it, but it helps test every part of the program. With good tools, it becomes easier to find and fix problems. It’s a smart way to make strong and error-free software.

If you want to learn more about this topic, you can refer to our Java course.

What is White Box Testing? – FAQs