Software errors can be very costly. An estimated $2.84 trillion was the cost of poor software quality to organizations in the United States alone in 2018. Although the number itself is shocking, the effect is not just money related. Bugs in software can lead to the loss of customers and their data, which is a major betrayal of trust.
So it becomes very clear that software testing has to be strong and thorough. However, testing happens in various forms and therefore not all testing is the same. If a software is going to be released to the market, it has to be tested from two different and opposite angles: the internal one of the developer who wrote the code, and the external one of the user who will use the software.
If you are new at quality assurance (QA) or software development, the language can be quite bewildering. You can overhear the teams talk about “glass boxes” and “closed boxes” and end up wondering which method is the one that is required. Generally, the answer is most likely “both,” however, to understand the rationale, you need to go a little deeper.
This article will demystify white box and black box testing concepts for you by using easy-to-understand metaphors and minimal technical jargon. We will uncover exactly which actions constitute the two testing techniques, list their advantages and disadvantages, and use relatable examples to help you determine which method suits your project needs.
What is White Box Testing?
A transparent glass box is what comes to your mind first? Through its walls, you can see all the mechanisms of the equipment – gears, wires, and circuits that work together. In case a gear gets stuck, you don’t just realize that one of the gears is broken, but you understand the real reason i.e. you have full visibility of the cause of the problem.
White Box Testing is a method of testing that peers through the software’s outer layer and looks at the internal coding, structure, and logic.
How It Works
White box testing (or clear box, open box, structural testing) involves having a detailed knowledge of the source code of the software being tested. The tester is most likely a developer who understands the programming language utilized in the making of the software.
They are not just checking whether the software works but also if the code is written efficiently. They scrutinize the various code paths. For instance, if a user selects “Login,” the code might follow Path A in the case of a successful login or Path B in the case of a failed login. A tester implementing white box testing prepares scripts to ensure that both Path A and Path B are present, functioning correctly, and do not have any security loopholes.
Advantages
- Code Optimization: Because the tester inspects the code directly, he/she can detect the areas where the code can be made more efficient. For instance, they can rework a function so that it consumes less memory or runs much faster.
- Removing Dead Code: Software ends up with “dead code” – lines of code which are not used anymore but still take up space – over time. White box testing identifies and removes such parts keeping the application light and fast.
- Early Detection: This kind of testing typically takes place at a very early stage of the development process (usually during Unit Testing). The savings in the cost and effort of fixing the bug after finding it at this stage is enormous.
Disadvantages
- High Cost and Skill Requirement: It is not possible to just employ anyone to work on white box testing. The testers must be competent developers who have an in-depth understanding of algorithms and code structures. Their time is costly.
- Time-Consuming: It is practically unfeasible to test all the possible code paths of a large software product. Striving to achieve 100% code coverage can drastically hamper the progress of the development.
Example Scenario
Consider one developer who wants to make a backdoor login page secure. They have to look at a particular code “if/else” loop.
- In case the database is connected, the password check will be executed.
- The system must log an error if the connection to the database fails.
The developer prepares the test which closes the connection to the database just to see if the code running under “Else” triggers the system to do the return correctly. Not browsing the user interface is their focus but the logic on the screen step by step.
What is Black Box Testing?
Next, visualize a non-transparent, black box. You have zero visibility into the box. You don’t know how the gears were set up or how the wires were connected and to which part. On the box, there is a set of buttons (inputs) and a display screen (output). If you were to press the button, the result on the screen has to be what you expect. The way the box processes the command does not interest you as long as the output is correct.
That is Black Box Testing. It gives a holistic view of the system. Testing with a black box means you only care about the software feature that you are using and not how it was implemented.
How It Works
Black box testing (also known as behavioral testing) looks at the software from the end-user’s perspective. The tester acts like a buyer. They don’t need to know whether the app was developed in Python, Java, or C++. Interaction with the user interface (UI) is the only way they can find out if the software performs the functions it is supposed to give.
They run the test by using the requirements as a benchmark. The requirement can state, “Pressing the ‘Add to Cart’ button should increase the total cart items by 1”. In such a case, the test would involve clicking the button and verifying the contents of the shopping cart. The presence of an extra item in the cart means the test has been successful while its absence means the test has failed.
Advantages
- No Coding Knowledge Needed: The testers don’t need to be developers. This opens up the pool of possible resources and developers can concentrate more on making the product.
- User Perspective: This method is perfect for surfacing User Experience (UX) issues. For example, a developer may write a piece of code that works perfectly on a technical level, but a black box tester might realize that the button is in a very confusing position or the text is so small that you can’t read it.
- Unbiased Testing: Generally, the developer and tester are different individuals, so there is a clear distinction. The tester is unaware of the expected working of the code because of which they are not “biased”; they only know how the code actually works.
Disadvantages
- Hidden Issues: Not being able to see the code means internal logic errors might be missed by the tester. The correct solution might be given by the app, but it takes 10 seconds for it to do so because of the poor coding—a black box tester might just think their internet is slow.
- Redundant Testing: If the tester isn’t cognizant of the code logic, a considerable amount of time may be wasted in testing scenarios which the code has already ruled out as impossible.
Example Scenario
Let’s return to the QA tester scene. They are dealing with the login screen. What happens inside the “if/else” statement or the database connection string don’t interest them. What they do is enter username and password wrong falsely and then they expect at least in one place, a red error message saying, “Invalid Password”.
The test goes fine if a message appears. They report a glitch if the application even crashes or logs them in anyway. Here, they don’t validate the mechanics but the behavior.
Major Differences: Comparing the Two Methods
There is a great need to see the two testing methods through the lens of various factors for one to get a clear understanding of what makes them different from each other.
Visibility
Visibility is the main difference between the two methods. White box testing is when the tester has access to the internal workings like the code, logical flow, and technical details of the software while in black box testing these elements are completely inaccessible to the tester. The tester is only concerned with the behavior of the software from the outside.
The Performer
Who performs the job? White box testing is almost always done by developers or specially trained programmers with strong development skills. They have a “builder’s mindset”. On the other hand, QA analysts are the ones who usually perform black box testing. They use the “user’s mindset”, which helps them to ensure that the product is understandable to the ones who buy it.
Granularity and Level
White box testing is usually very detailed. Unit testing exemplifies it, which hardly tests any higher-level aspects but only small individual pieces of code (such as a single function). Black box testing is concerned with the big picture. It examines complete workflows like registering a user, looking up a product, and making a purchase.
Implementation Summary
The implementation differences can be represented barely like this:
- White Box: Structural Testing. (Is the code built correctly?)
- Black Box: Functional Testing. (Does the app work correctly?)
To sum up, the biggest difference between white box and black box testing is whether the test engineer can look at the code or not. One method is about ensuring the engine is well-built while the other is focused on ensuring the car runs smoothly.
Real-World Case Studies
Let’s now investigate through examples how white box and black box testing help businesses avoid costly mistakes.
Case Study 1: Banking App Security (White Box Focus)
Scenario: The bank is developing international money transfer functionality. The fundamental condition is that if User A sends $500 to User B, then the system should precisely reduce User A’s account by $500 and credit User B’s account with $500.
Application: A black box tester could verify that the balance on the screen changed. However, for a banking app, that is not enough. The developer does white box testing on the transaction script. They check the code to see if the decimal markup is handled correctly (so that no fractions of pennies are lost). More importantly, they look for vulnerabilities in the code that would allow a hacker to inject malicious code during the transfer and divert the funds. Only by looking at the code internally can such a level of security be guaranteed.
Case Study 2: E-Commerce Checkout (Black Box Focus)
Scenario: The online clothes store is getting ready to offer a brand new checkout flow. They want to be sure that customers have a hassle-free experience when ordering products.
Application: A white box test verifies that the triggering of a correct database entry happens when the “Buy Now” button is clicked. However, the entire sale still depends on the buyer. When the black box tester is simulating a shopper, they only have the cart to which the items are added, the shipping address, and the payment feature. During their journey, they notice that it takes 5 hours for the confirmation email to arrive after they press “Pay”. Or they find out that on mobile screens, the “Place Order” button is hidden below the fold. These are problems that can’t be detected by looking at the source code but can be easily spotted by black box testing.
When to Use Each Testing Method
Here is the thing, choosing between these two methods is not frequently an “either/or” kind of answer; instead, it is “when” the question is asked.
Project Phase
The choice of the test should be determined by the set of processes that are involved in the software development lifecycle (SDLC).
- In the Beginning: White box testing is the appropriate choice at coding stages (Unit testing and Integration Testing). During these phases, developers are writing the logic and polishing it. Spotting syntax errors and logic loops here is very time-saving.
- At the End: Black box testing is the way to go during System Testing and Acceptance Testing. It is necessary to check that every component works together before the software is released to the end-user or the client.
Resource Availability
Resources in project management are always limited. If you count hundreds of developers but just a handful of QA people, then you might depend more on automated white box unit tests to a greater extent. On the other hand, if your dev squad is pretty small and just focuses on shipping features, you could count on an external QA team to do solid black box testing to find those issues that developers overlooked.
The Hybrid Approach (Gray Box)
It is possible to compromise and have some of the advantages of both worlds, and this is called Gray Box Testing. The tester has a certain level of internal code knowledge, such as the database schema or algorithms but still conducts the test from the UI perspective. It is especially handy for integration testing when you are required to verify how two different modules interact with each other.
The Importance of Expertise in Testing
Many think that software testing just merely means “clicking on the screen randomly until the software breaks.” This is a gross misconception because effective testing mandates problem-solving skills and a high level of expertise.
It is not only those who create content that have to follow Google’s E-E-A-T (Experience, Expertise, Authoritativeness, and Trustworthiness) guidelines, but also transferring how your organization or company gains trust in your software is one of the ways to apply it.
- Experience: A tester who knows “everything” can very quickly recognize the common hiding spots of bugs. Veteran black box testers are aware that unpredictable users do many strange things like double clicking the “Submit” button and hence besides doing test for normal cases, they also test for such cases.
- Expertise: White box testers need technical expertise which is encapsulated in their profound knowledge about code efficiency and security protocols necessary for the robustness of the software.
- Trustworthiness: Combining the awesome experience and the high level of expertise, you get to create a very trustworthy product. In the case of a bank being hacked due to the failure of its banking app, it is the trustworthiness that is lost, not the product.
Testing using a balance of both white and black box methods diminishes the need for heavy and costly patches after the release. You can be assured that the software is both technically sound (White Box) and intuitively functional (Black Box).
Conclusion
In summary, the difference is quite simple: White Box testing is about code logic, clarity, and making the structure of the code visible externally. This is the mechanic working on the motor. Meanwhile, Black Box testing is mainly concerned with the external features, user interaction, and discovering behavior. This is the driver taking the vehicle out for a test drive.
Neither of the two methods is inherently “better”. On the contrary, there is a recipe for disaster when only one method is relied upon. If the product has perfect code that is impossible to use, it will be a failure. On the other hand, if a product is pretty rolling with a user-friendly interface but packed with security holes in the code, it is going to fail as well.
Simply put, the dissimilitude between white and black box testing does not necessarily imply a rivalry. Instead, it is about the proper usage of the right tool at the right moment and for the right task.
For those of you building software right now, you should be asking your project questions like “Am I spotting bugs early enough?” or “Is my user experience smooth?”. Perhaps you should hire a QA specialist to appraise your testing lifecycle if you find that you do not know which strategy to give preference to.
