Black Box Testing: A Complete Overview

Laws are like sausages; it is better not to see them being made.”

This quote, often attributed to Otto von Bismarck, is quite relevant to this article. Sometimes it’s advantageous to assess applications without understanding their intricate details. This approach is known as black box testing, which is the focus of this article.

This article explores black box testing, covering what it is, its essential elements, different techniques, examples, benefits, and tools that can help implement such tests in your Software Development Life Cycle (SDLC).

What is Black Box Testing?

Black box testing (sometimes written as black-box testing) is a form of software testing in which the QA verifies the software “in a black box,” i.e., not knowing the internal mechanisms or code structure of said software product. The intent is to simply check how an app works from the perspective of a non-technical end-user.

The tester checks the software functionalities without any concern for internal details or implementation strategies. They simply provide the input (by initiating different user actions) and observe the output (response time, usability, reliability) generated by the system. In other words, they use the app as a regular customer and report on its workings.

These tests can cover various aspects of the software, such as functional behavior, system response, user interface, databases, dependencies, and integration with third-party systems. However, the primary focus remains on validating the outputs for different inputs without considering the internal structure

A common example of black box testing is Dynamic Application Security Testing (DAST), a technique used to verify product quality on the level of compliance and security.

Elements of Black Box Testing

• Independent Tests: Individuals running black box tests are generally not attached to the development team. This gives them a fresh set of eyes, which is essential for this form of test.
• Requirements-based Tests: Test cases are built on the backs of the app’s requirements and predetermined specifications. They do not take into account the app’s backend systems.
• Functional Tests: Black box tests primarily focus on verifying the software’s functionality according to its requirements. The goal is to determine whether the system behaves as expected for given inputs, which can encompass a variety of scenarios beyond typical end-user interactions.
• Unaware of Internal Code: Testers should have zero knowledge of the app’s internal code, design, or architecture. It’s ideal if said testers also have zero technical knowledge in general (unless using the app requires some expertise).

Black Box Testing Types

Generally, black-box testing incorporates the following forms and methodologies:

• Functional Tests: As the term suggests, functional tests verify the primary functions of the app under test. It focuses on inputs, outputs, and interaction between the app and the user.
• Non-Functional Tests: These tests focus on aspects other than the core functionality, such as usability, scalability, security, reliability, and performance. They assess how the system performs under different conditions rather than verifying specific features.
• User Interface (UI) Tests: These tests validate the user-facing elements of the app — menus, buttons, forms, layouts, etc.
• Usability Tests: These tests scan through the app’s user-friendliness and learning curve. Metrics important for usability are navigation, ease of learning, aesthetic appeal, accessibility, and the overall user experience.
• Ad-hoc Tests: These tests are informal and unstructured. Testers approach the app exactly as an end user would and try to use various features based on intuition and experience.
• Compatibility Tests: These tests examine and monitor how an app operates on different browsers, browser versions, device models, screen sizes, resolutions, operating systems, and network configurations.
• Security Tests: These tests verify the strength and efficacy of security mechanisms implemented to protect user data and its app integrity.
• Localization Tests: These tests observe the app’s performance in different regions and environments. It evaluates that the right adjustments are made in the app’s language and other features — adjustments required to align with different cultural and regional expectations.

Black Box Testing Techniques

Black box testers have zero knowledge of the application’s internal structure and thus require some direction in order to cover all relevant inputs and user scenarios. The following techniques help provide such direction:

• Equivalence Class Testing: In an application, different inputs may follow the same control flow. Let’s say an app is only meant for adults and will restrict access to anyone under 18. Similarly, an app can only be accessed in certain locations, and anyone outside those zones will be restricted.
• Equivalence class testing or equivalence partitioning checks that the relevant classes produce the same results, and testing for one value within that class.
• Let’s say that a form to verify user age accepts inputs between 18 and 80. The equivalence partitions would be:

1. Valid partition: 18–80 (e.g., age 32)
2. Invalid partition: Below 18 (e.g., age 12)
3. Invalid partition: Above 80 (e.g., age 85)
4. Boundary Value Evaluation: Boundary values refer to inputs that cause the app’s mechanisms to sift from one control flow to another. Going by the above example, ages 17 and 18 and boundary values. Since 17 is too young and 18 is the right age, the control flow shifts between these two values. Boundary value testing must be formulated to check that the system handles such edge cases appropriately.
5. Decision Table Testing: Certain applications make operational decisions based on multiple inputs in tandem. For instance, let’s say the above app allows login for users who are both 18+ and located in specific locations.
6. In this case, decision table tests will feed multiple input combinations and check outcomes to see if the app behaves accurately.
7. State Transition Evaluation: Certain applications are designed to change their operational state when met with certain conditions. An example of this is the app locking a user’s account after three failed authentication attempts. State transition evaluation verifies that such a state change occurs under the right conditions every time they are met.
8. Error Checking: In this type of black box testing, QAs check for common errors developers can make when coding the app. Most commonly, these checks cover input sanitization and enforcement of input assumptions (laid out in the requirements documents).

For example, a question error checking can answer “Did the developers properly handle an input of zero in the numeric field?” or “Did they restrict the number of characters that can be used to set a username or password?

Examples of Black Box Testing

Black Box Testing Example #1

You’re testing the checkout process of an e-Commerce website. Your job, as a black box tester, is to assess the quality of the user experience in this workflow, with no access to the underlying code.

Test steps include:

• Adding an item to the cart.
• Clicking the button to move to the processing page.
• Initiate payment.
• Verify that the payment gateway successfully processes the transaction and the amount is correctly deducted from the bank account or credit account.
• Check if the app/site also notifies you of a completed order.

As the test progresses, you can also verify how the system handles errors by entering incorrect information. Check that clear error messages are displayed with prompts for corrections.

Black Box Testing Example #2

You’re testing a login form that should only accept between 6 and 12 characters.

Test Steps:

• Enter 5 characters. Result should be an “invalid input” message.
• Enter 6 characters. Result should be a successful login.
• Enter 17 characters. Result should be an “invalid input” message.
• Enter 8 characters. Result should be a successful login.

Black Box Testing Example #3

You’re testing an online shopping cart that accommodates between 1 and 10 items.

Test Steps:

Add 0 items. Result should be an “invalid input” message.
Add 1 item (valid). Result should be a valid response.
Add 7 items. Result should be a valid response.
Add 12 items. Result should be an “invalid input” message.
Test values at the boundaries (0 or 11, in this case). This ensures accurate edge case handling.

Black Box Testing Example #4

You’re testing a banking system’s transfer capabilities. The conditions are:

• The system charges a $1 fee when transferring less than $1000.
• No fee is charged for transfers of $1000. In each case, the system must also check the account balance for sufficient funds, dictated by the transfer request.

Test Steps:

• Transfer $500 from a bank account with a $2000 balance. Result should be a successful transaction.
• Transfer $1500 from a bank account with a $2000 balance. Result should be a successful transaction.
• Transfer $700 from a bank account with a $500 balance. Result should be an error message mentioning insufficiency of funds.
• Transfer $900 from an account with a $300 balance. Result should be an error message mentioning insufficiency of funds.

Black Box Testing Example #5

You’re testing an e-commerce website. The conditions are:

• The customer must be logged in to make purchases.
• The customer gets a discount only after their cart amount is higher than $200.
• The customer logs in and adds items worth $120. This cart should not receive the discount, but purchase should be successful
• The customer does not log in and adds items worth $150. The cart should not receive the discount and should not be able to complete the purchase.
• The customer logs in and adds items worth $370. The cart should receive a discount, and the purchase should be completed.

Black Box Testing Example #6

You’re testing a site’s file upload capability. The conditions are:

• It only accepts PDF files.

• It only accepts files up to 5 MB in size.
  Test Steps:

• You try to upload a 6 MB file. It does not work, and an error message is displayed.

• You try to upload a .rtf file. It does not work, and an error message is displayed.

• You try to upload a PDF file weighing 4 MB. It works, and the file is uploaded.

Black Box vs White Box Testing

To understand the nuances of black box testing, it is helpful to compare it with its counterpart: white box testing.

Benefits of Black Box Testing

Here’s why black box testing should be keyed into every SDLC:

• Provides an unbiased perspective on the software under test. Since testers have no understanding of how the software works, they have no bias. They simply scan through the app as an actual user would and conduct tests with fresh eyes.
• It helps examine the product from the user’s eyes and validates the user experience. This is absolutely central to ensuring an app’s success.
• Since testers don’t need technical knowledge to run these tests, it is easier and more affordable to recruit them. In fact, it’s ideal if you can find actual users as testers.
• Test cases for black box testing are easier and faster to create because you don’t have to account for code structure and content. Simply outline common usage scenarios, and you have your test cases ready to go.
• Since black box tests are independent of the code specifications, it can be adapted to most test scenarios and software types. From unit testing to system testing to acceptance tests, the black box approach is equally effective.

Conclusion

In conclusion, black box testing is an essential method in software quality assurance that focuses on evaluating applications from a user-centric perspective without understanding their internal structures. By simulating real-world scenarios, black box testing helps ensure functionality, usability, and performance align with user expectations. This approach enhances the app’s reliability and user experience, making it a valuable addition to the SDLC. Leveraging tools like TestGrid further simplifies the process by offering a cloud-based infrastructure and AI-powered automation, enabling efficient and scalable testing across diverse devices and environments.

Source: This blog was originally published at testgrid.io