Black Box Testing and White Box Testing

Black Box Testing and White Box Testing

Black box and white box testing are distinct methodologies with opposing objectives. However, they can complement each other to improve testing effectiveness. Black box testing evaluates an application from the user's perspective, while white box testing examines the code and internal design.

Black box Testing

Black box testing is a way of testing software without looking at its internal code or design. Testers check if the software works as expected by using the requirements and specifications. They enter data, watch the outputs, and see how the system responds, including how fast and reliable it is.

This method can be used at many levels of testing, like unit, integration, system, and acceptance testing, but it’s mostly used in higher-level tests. Testers don’t need coding knowledge—they just focus on whether the software does what it should from the user’s perspective.

It’s also called specification-based testing or closed box testing because it only looks at what the software does, not how it does it.

Types of black box testing

Black box testing encompasses various types, each tailored to address specific aspects of the software. Here are some common types of black box testing.

Functional Testing
This testing checks if the software works according to its requirements. Testers give inputs and check if the outputs are correct.
For example, testing a login page:

• Enter valid username and password, then click "Login" to see if it logs in and redirects properly.

• Enter wrong credentials and check if an error message appears.

• Leave fields empty and verify that the correct error message shows up.
  This ensures the login works correctly in different cases.

Non-Functional Testing
This tests how well the software performs, rather than what it does. It looks at things like speed, usability, reliability, security, and how many users it can handle at once. For example, checking if the system can handle many users logging in at the same time or if the interface is easy to use.

Regression Testing
When the software is updated or fixed, regression testing checks that old features still work properly. It retests existing functions to make sure nothing broke after changes were made.

Black box testing techniques

Black box testing employs several techniques to ensure comprehensive test coverage

Equivalence Partitioning
This technique divides input data into different groups or partitions where all values are expected to be treated the same by the system. Instead of testing every possible input, you test just one value from each group, saving time while still covering all scenarios. For example, if a system handles ages below 18 differently from ages 18 and above, you test one age from each group rather than every age.

Boundary Value Analysis
This method focuses on testing inputs at the edges or boundaries of allowed input ranges because errors often happen there. For example, if valid ages are between 18 and 30, test cases would include values like 17, 18, 30, and 31 to check how the system handles inputs just outside and exactly at the limits.

Decision Table Testing
Decision table testing is a method that uses a table to organize different combinations of inputs and their expected outcomes. This helps testers cover all possible scenarios systematically and reduces the chances of missing any case.

For example, in a login system where users enter an email and password:

• If both email and password are correct, the user is allowed to access the home page.
• If either is incorrect, an appropriate error message is shown.

A decision table for this might look like:

Email Correct?	Email Incorrect?	Password Correct?	Password Incorrect?	Outcome
Yes	No	Yes	No	User goes to home page
Yes	No	No	Yes	"Incorrect password"
No	Yes	Yes	No	"Incorrect email"
No	Yes	No	Yes	"Incorrect email"

 

Using decision tables helps testers ensure they test every possible input combination and the related system behavior efficiently.

State Transition Testing
This testing checks how a system changes states based on different inputs. It ensures the system behaves correctly during each transition.

For example, in an ATM:

• Starts at Waiting for card insertion.
• Moves to Card Inserted when a card is inserted.
• Goes to PIN Entered after correct PIN input.
• Proceeds to Transaction Initiated when a transaction is selected.
• Ends at Transaction Completed after finishing the transaction.

It tests all possible states and transitions to catch errors in state changes.

Error Guessing
Error guessing is an informal testing technique where testers use their experience and intuition to find defects that formal tests might miss. It relies on knowledge of common developer mistakes and software behavior to guess where errors might occur. For example, testers might check how the system handles null values or looks for security issues in user input. This approach helps find hidden bugs and improve overall software quality.

Exploratory Testing
Exploratory testing is an informal approach where testers design and execute tests at the same time, without pre-written test cases. Testers use their knowledge and skills to explore the software, find bugs, and check functionality in real-time. This method helps uncover issues missed by structured testing and speeds up feedback and documentation. It is especially useful for new team members learning the system quickly or when fast testing and feedback are needed.

White box Testing

White box testing focuses on examining the internal workings of a system, such as the code, architecture, and integration with other systems. It is important in automated processes like continuous integration and delivery (CI/CD). This testing uncovers security issues, code paths, and vulnerabilities that black box testing might miss. However, it requires testers to have strong skills in coding and understanding system design. Combining white box with black box testing gives a more complete evaluation of software quality.

Types of white box testing

White box testing encompasses various types, each designed for specific purposes within the testing process.

Unit Testing:
Unit testing verifies individual parts of software to ensure they work correctly. It’s done early and usually automated to catch problems quickly before combining components.

Integration Testing:
Integration testing checks how different parts of a software work together. It finds problems that happen when modules are combined and makes sure they work correctly as a group. For example, it tests if a web app and database communicate properly. This testing happens after individual parts are tested separately.

Difference between Black box Testing and White box Testing

Aspect	Black box testing	White box testing
Technical knowledge	Requires minimal technical knowledge	Demands substantial technical expertise
Programming skills	No programming skills required	Necessitates programming proficiency
Understanding system details	Focuses on system behavior	Requires in-depth understanding of code
Outsourcing	Easily outsourced	Often performed in-house
Test design efficiency	Quick test design as it mimics user behavior	May involve longer test design processes
Code coverage	Limited code coverage	Achieves comprehensive code coverage
Cost	Cost-effective	Incurs higher costs due to specialists
Root cause analysis	Challenging to pinpoint issues	Easier identification of root causes
Testing perspective	Focuses on validating user experience	Analyzes code structure, conditions, paths
Reporting detail	Provides concise reports	Generates detailed, granular reports
Time efficiency	Streamlined testing process	Requires more time for thorough examination
Algorithm testing	Unsuitable for algorithm testing	Well-suited for algorithm validation
Tester profile	Typically performed by testers	Primarily conducted by developers
Time requirement	Relatively quicker testing phase	Demands more time for comprehensive checks
Basis of testing	Rooted in external expectations	Based on internal coding and structure
Purpose	Validates business needs and requirements	Ensures code quality and integrity.
Drawbacks	Difficult to automate; potential missed paths	Higher costs
Error detection	Focuses on system behavior	Detects hidden bugs, optimizing code

In short, White box testing focuses on the internal structure and code of the software, helping find hidden issues and improve security. Black box testing checks the software’s functionality from the user’s perspective without looking at the code. Together, they provide a complete approach to ensure software quality.