The Beginners Guide to White Box Testing

Software testing refers to a systematic process of verifying that the generated product performs as expected and guaranteeing that it does not contain any unwelcome surprises once shipped.

The cost of software testing is significantly less than the expense of having a severe bug discovered after the product has been sent and then fixing it. However, the loss in customer happiness and loyalty is the highest cost of finding a bug after the product has shipped.

Your clients may immediately switch to a competitor, and the story will abruptly stop. 

The process of developing and testing software is essential.

It ensures quality, dependability, and reduced risk. In addition, thorough testing assures effective performance and satisfied consumers, which translates to a successful business.

A software product can be evaluated for a variety of criteria and in a variety of ways.

However, on a fundamental level, the software can be considered for its intended functionality, i.e., whether it performs as intended.

White Box testing is a significantly more extensive product testing. Here, you test more than just the functionality. Compared to the black box, the box is now translucent or, to put things in perspective, it is now white. As a result, you can observe the product's inner workings.

All statements, conditional loops, input flow, and more are displayed.

Therefore, you will require an experienced programmer or a testing specialist who is well-versed in programming languages and coding procedures for White Box testing. This article will focus on white box testing.

What Is White Box Testing?  

White box testing is a technique that permits testers to examine and verify the inner workings of a software system, which consists of its code, infrastructure, and connections with external systems.

White box testing is an integral component of the automated build processes of a contemporary Continuous Integration/Continuous Delivery (CI/CD) software development pipeline.

Static Application Security Testing (SAST) frequently mentions white box testing, an approach that automatically checks source code or binaries and provides feedback on potential vulnerabilities and flaws.

What Does White Box Testing Focus On? 

White box testing can target any of the following issues with an application's source code:

Security Gaps and Vulnerabilities

Security holes are program components that make an application susceptible to attack. Not securing your apps against injection attacks, for instance, may leave a security hole in the program, which an attacker could exploit one day to compromise client data.

White Box Testing determines if the application was programmed using security best practices and if the code is vulnerable to known security threats and exploits.

Checks for Broken/ Poorly Structured Programming Paths

There are specific coding standards that, if not adhered to, may not result in an error but may lead to unexpected behavior in certain circumstances.

Also, coding constructs such as conditions may lead to unforeseen outcomes if left unchecked or the programmer has not examined all possible values for a condition.

White box testing helps reveal incomplete and faulty program structures, finding redundant, flawed, or inefficient conditional logic.

Expected Output

This entails evaluating all possible inputs to a function to determine whether or not it always produces the expected result.

Loop Testing

A program will always fail if a loop construct is not written correctly and causes it to encounter an infinite loop.

Since nested loops can quickly become unmanageable mazes of code, it's preferable to avoid allowing them wherever possible in favor of more straightforward constructions.

White Box Testing evaluates the efficiency, conditional logic, and correct handling of local and global variables in single loops, concatenated loops, and nested loops.

Data Flow Testing (DFT)

This is the process of tracing variables and their values as they flow through the code to identify variables that are not appropriately initialized, declared but never utilized, or improperly modified.

To determine if there are competing variable names or if program constructs are altering the value of a variable mistakenly, it is advisable to track a variable's life cycle from its declaration until it is disposed of.

Verifying Expected Outcomes

One of the most critical aspects of testing is determining whether the desired outcomes are being achieved.

White Box Testing is carried out to ensure that the expected results of a software program are achieved.

Verification of Every Statement and Function Call

White-box testing requires verifying each statement within a function to ensure the program's integrity.

Types of White Box Testing

The two most prevalent forms of white box testing are Unit Testing and Integration Testing.

1. Unit Testing

In Unit testing, the application is viewed as the cohesion of multiple components or modules. Therefore, each module's control data, methods, and flow are independently verified. Typically, developers write automated tests to confirm that an application component meets design requirements.

The programming style is a crucial determinant of a unit component.

In an object-oriented style, for instance, a unit becomes a class and its interface. Execution, operations, and mutation testing are all kinds of unit testing.

2. Integration Evaluation

During integration testing, numerous related individual units or modules are examined as a group. It assesses how well the constituent units conform to functional criteria and identifies any flaws in the interaction between the various elements.

Integration testing is subdivided into Top-Down, Bottom-Up, and Hybrid approaches.

Other forms of white box testing include:

Mutation Testing

This form of unit testing verifies the code's resilience and consistency by designing tests, making minor, random changes to the code, and determining whether or not the tests still pass.

White Box Penetration Testing

In this type of white box testing, an ethical hacker appears as a knowledgeable insider and attempts to attack an application using extensive knowledge of its code and environment. 

Static Code Analysis

Automatically discovers vulnerabilities or coding flaws in static code using predetermined patterns or machine learning.

Steps to Perform White Box Testing

White Box testing requires the tester to perform several tasks.

1. Determining What Must Be Tested

White box testing encourages examining every component of the selected instance. Hence a fewer number of identified pieces is preferable.

Existing flaws become evident after these are put to the test.

The features and components are subjected to repeated testing to ensure they function as planned. Small components are extracted and evaluated, and the next component is extracted when the objective is met.

It is also essential that the tests are energy efficient, meaning that the quantity of energy expended is proportional to the result obtained.

2. Organizing the Flowchart

The flowchart depicts all possible and conceivable paths. These pathways may correspond to any feature, module, or component. It is performed to identify the testing's scope.

3. Developing Test Cases for All Paths

Create test cases for each possible path after mapping the various paths. After creating the test cases, they are executed.

4. Execute It

This is the testing execution phase, where test cases are executed. Then, the execution stages can be repeated to confirm the test results.

White Box Testing Techniques 

A primary objective of white box testing is to cover the source code as thoroughly as possible.

Code Coverage analysis is a prevalent white box testing method.

Code Coverage, often known as test coverage, is a metric that indicates how many statements or lines of code have been executed.

Using notions such as statement coverage, branch coverage, and path coverage, it is feasible to determine how much of an application's logic gets to run and tested by the unit test suite.

We would further discuss these concepts below:

Statement Coverage

Statement coverage seeks to assess the maximum number of executable statements across a module or feature, as its name suggests.

This white box testing technique ensures all executable code statements are executed and tested at least once. For instance, if multiple conditions exist in a block of code, each of which is utilized for a given range of inputs, the test should evaluate each capacity of inputs to confirm that all lines of code are performed.

Statement coverage aids in the identification of new statements, unneeded branches, missing statements referenced by a portion of the code, and dead code left over from prior versions.

Decision coverage / Branch Coverage

Branch coverage divides the code into branches of conditional logic and guarantees that unit tests cover each branch.

This coverage technique maximizes testing on each branch, such as an if statement or a loop.

Path Coverage

Path coverage pertains to linearly independent code pathways. In a path coverage technique, the tester writes unit tests to execute as many of the program's control flow paths as possible. The purpose is to detect broken, duplicated, or inefficient pathways.

Multiple Coverages

Testing every potential outcome combination of a condition or a decision statement.

Other code coverage methods include Finite State Machine, Path, Control Flow, and Data Flow coverage.

Advantages of White Box Testing 

In addition to the benefits that testing provides, White box testing provides:

• Simple script automation for testing.
• Since code is examined one statement at a time, it is greatly optimized.
• Extremely exhaustive testing with all pathways covered.
• Unit testing can begin relatively early in the life cycle of an application, minimizing the likelihood of mistakes appearing late in the life cycle.

Disadvantages of White Box Testing

Like every other concept, there is; white box testing also has its disadvantages.

Here are some of the highlighted disadvantages:

• In comparison to other types of testing, white box testing is a complex, time-consuming, and expensive endeavor.
• For white box testing, additional and highly qualified resources are required.
• It might be costly.
• Typically, the tests are not exhaustive; hence, they may contain errors.
• Testing demands a resource with experience because it involves technical understanding.

White Box Testing Example

Now let us consider this simple pseudocode:

INPUT USER, PERMISSION

 

IF USER IS LOGGED IN AND USER.HAS(PERMISSION)

GRANT ACCESS

PRINT("ACCESS GRANTED") 

ELSE

RESTRICT ACCESS

PRINT("ACCESS DENIED")

 PRINT("COMPLETED")

For the above pseudocode, it is a typical scenario of a user navigating an application ( in this case, a blog site) with the intent to make a publication. The test code applies to questions like:

• Is this user logged in correctly?
• Does this user have the 'CREATE_POST' permission

If both conditions are met, GRANT ACCESS
If not, RESTRICT ACCESS

At the end of the operation, 'COMPLETE'

White Box Testing Tools

The various white box testing tools include:

• EclEmma
• PyUnit
• HTMLUnit
• CppUnit

Conclusion

Suppose your application is in a high-risk industry, such as avionics or medical devices.

In that case, it is best to have it thoroughly tested using white-box techniques.

Black box testing alone is insufficient for maximum test coverage. We need to use black box and white box testing techniques to cover the most defects.

White box testing, when done correctly, will undoubtedly improve software quality. It is also beneficial for testers to participate in this testing because they can provide the most "objective" opinion about the code.