Black Box Testing

Software testing is an essential process in the development of any software system and black box testing is a widely used method for ensuring that software meets the desired quality standards. Black box testing is a technique in which testers examine the behavior of a software system without knowing the internal details of the code or system architecture. Instead, they focus on the input and output of the software system and evaluate how well the software performs in response to different inputs. Black box testing is an important tool for verifying that software meets user requirements and can help identify defects and vulnerabilities that could impact the user experience.

In this article, we will explore the concept of black box testing in more detail, including its benefits and limitations and discuss some common techniques used in black box testing.

Definition of the Black Box Testing

Definition

Black box testing is a method of software testing in which the internal workings of the software are not known to the tester. In other words, the tester is only concerned with the inputs and outputs of the software and does not have access to the source code or internal structure of the software.

The purpose of black box testing is to ensure that the software meets the specified requirements and works as expected from a user's perspective. Testers use a variety of techniques to perform black box testing, including equivalence partitioning, boundary value analysis, decision table testing and state transition testing.

Type of Black Box Testing

Black box testing is a widely used method for software testing. There are two main types of black box testing techniques that are commonly used:

• Functional Testing
• Non Functional Testing

Note - Will will discuss in the details in the coming chapters.

Black Box Testing Techniques (Most Important)

There are many types of black box testing techniques-

• Boundary Value Analysis
• Equivalence Partitioning
• Decision Table Testing
• State Transition Testing
• Graph-Based Testing Methods
• Error Guessing
• Comparison Testing

Comparison Testing Let's explain each one by one-

1. Boundary Value Analysis

This technique involves testing the software system using the boundary values of the input domain, as these values are often more likely to cause errors or issues. Testers evaluate the behavior of the software system when input values are at the minimum, maximum, or just beyond the boundaries of the input range.

Example-

• Scenario: Let's say we have an input that accepts integers between 0 and 100 (inclusive) as input, and performs some calculations based on the input value.

To perform Boundary Value Analysis, we would choose values that are just above and just below the boundaries of the input domain, as these values are more likely to cause errors or issues.

In this case, we would choose the following values:

Boundary Value Analysis for above scenario (min input 0 and input 100)-

• Input value of -1 (just below minimum value)
• Input value of 0 (minimum value)
• Input value of 1 (just above minimum value)
• Input value of 99 (just below maximum value)
• Input value of 100 (maximum value)
• Input value of 101 (just above maximum value)

We would then test the software system with each of these input values and analyze the results to ensure that the software system behaves correctly at the edges of the input domain.

2. Equivalence Partitioning

This technique involves dividing the input domain of the software system into equivalent partitions or groups, and testing the system with representative values from each partition. This helps to ensure that all the possible inputs are tested without having to test every individual value.

Example-

• Scenario: Let's say we have a software application that requires users to enter their credit card number. The credit card number is a 16-digit numeric value.

We can use Equivalence Partitioning to divide the input values into three partitions:

• First partition containing valid input values,
• Second partition containing invalid input values that are too short
• Third partition containing invalid input values that are too long.

Equivalence Partitioning for the above scenario in detail-

1- First partition (16 digit) For the partition of valid input values, we can select representative values such as 1234567890123456, 5555666677778888, and 9876543210987654 to test if the software correctly accepts them as valid input.

2- Second partition (<16 digit) For the partition of invalid input values that are too short, we can select representative values such as 12345678901234 and 555566667777888 to test if the software correctly rejects them as invalid input.

3- Third partition (>16 digit) For the partition of invalid input values that are too long, we can select representative values such as 12345678901234567890 and 5555666677778888999900001111 to test if the software correctly rejects them as invalid input.

By using Equivalence Partitioning to identify representative input values, we can ensure that the software is properly handling input values across the entire input domain. This approach can help identify defects and ensure that the software behaves correctly and consistently for all users.

3. Decision Table Testing

This technique involves creating a table that lists all possible combinations of inputs and their corresponding outputs, and testing the software system with each combination. This helps to ensure that all possible combinations of inputs are tested.

Example-

• Scenario: The scenario is a user wanting to buy a product online.

The rules are-

• The user is logged in,
• Has an item in their cart
• Has sufficient funds
• The actions are to allow the purchase or display an error message.

Scenario:	User wants to buy a product online
Rules:	Rule 1: User is logged in
	Rule 2: User has item in cart
	Rule 3: User has sufficient funds
Actions:	Action 1: Allow purchase
	Action 2: Display error message

Here is the Decision Table for above scenario-

Scenario:	Rule 1 (User is logged in)	Rule 2(User has item in cart)	Rule 3 (User has sufficient funds)	Action
1	true	true	true	Action 1 (Allow purchase)
2	true	true	false	Action 2 (Display error message)
3	true	false	-	Action 2 (Display error message)
4	false	-	-	Action 2 (Display error message)

The table lists all possible combinations of the rules and their corresponding actions.

For example,

• In scenario 1, all three rules are true, so the action is to allow the purchase.

• In scenario 2, rule 3 is false, so the action is to display an error message and all others scenario like that.

This table can be used to identify any gaps in the testing coverage, ensuring that all possible combinations of rules and actions are tested.

4. State Transition Testing

This technique is used to test software systems that have a defined state, such as a state machine or a control flow diagram. Testers use test cases to evaluate the behavior of the software system as it transitions between different states.

Example-

• Scenario: Let's say we have a software application that allows users to create and manage appointments.

The application has three states:

1. Not Scheduled
2. Scheduled
3. Completed

Users can perform the following actions to transition between states:

1. Schedule an appointment from "Not Scheduled" state to "Scheduled" state
2. Cancel an appointment from "Scheduled" state to "Not Scheduled" state
3. Complete an appointment from "Scheduled" state to "Completed" state
4. Cancel a completed appointment from "Completed" state to "Not Scheduled" state

Note- Cobine both above States and Actions in below table-

State	Action	New State
Not Scheduled	Schedule	Scheduled
Scheduled	Cancel	Not Scheduled
Scheduled	Complete	Completed
Completed	Cancel	Not Scheduled

To perform State Transition Testing, we would create a state transition diagram that shows the possible transitions between states based on user actions: -

Test Cases for above scenario-

To test this application using State Transition Testing, we would select test cases that cover all possible state transitions and verify that the application behaves correctly for each one. For example, we could select the following test cases:

1. Test case 1: Schedule an appointment and verify that the state changes from "Not Scheduled" to "Scheduled"
2. Test case 2: Cancel a scheduled appointment and verify that the state changes from "Scheduled" to "Not Scheduled"
3. Test case 3: Complete a scheduled appointment and verify that the state changes from "Scheduled" to "Completed"
4. Test case 4: Attempt to cancel a completed appointment and verify that the state remains "Completed"

By testing all possible state transitions, we can ensure that the application behaves correctly and consistently for all users. State Transition Testing is a powerful technique for testing software that involves complex state-based behavior.

5. Graph-Based Testing Methods

This technique involves using graphs, such as flowcharts or decision trees, to represent the software system's behavior and then creating test cases to cover all possible paths through the graph.

Example-

• Scenario: let's say we have a web application that allows users to search for and purchase products.

The application has several pages, including a homepage, search results page, product details page, and checkout page.

The following is a flowchart that represents the process a user follows to purchase a product:

Test Cases for above scenario-

Using this flowchart, we can design test cases that cover all possible paths through the application, such as:

1. Navigate from the homepage to the search results page, enter a search term, and verify that relevant results are displayed.
2. Navigate from the search results page to the product details page, verify that the correct product information is displayed, and add the product to the cart.
3. Navigate from the cart to the checkout page, enter valid payment information, and verify that the order is successfully processed.
4. Navigate from the confirmation page back to the homepage and verify that the user is logged out.

By using a graph-based approach, we can ensure that we are testing all possible paths and interactions within the system, helping to uncover defects and improve overall software quality.

6. Error Guessing

This technique involves using the tester's intuition and experience to identify potential errors or issues in the software system, and then creating test cases to target those areas.

Example-

• Scenario: For example, let's say we have an e-commerce website where users can place orders for products. An experienced tester might guess that errors are likely to occur during the checkout process, so they would design test cases to deliberately enter invalid or unexpected data, such as entering a non-existent address or attempting to purchase an out-of-stock item.

The tester might also guess that errors are likely to occur when the website is under heavy traffic, so they might design test cases to simulate multiple users accessing the website simultaneously or using the website on different types of devices.

Error guessing can be a highly effective testing technique when performed by experienced testers who have a deep understanding of the application and its potential vulnerabilities. However, it can also be subjective and difficult to reproduce, which is why it is often used in combination with other testing techniques.

7. Comparison Testing

Comparison Testing is a type of Black Box Testing that involves comparing the output of a system with a pre-defined set of expected results. The objective of Comparison Testing is to ensure that the output generated by the system is accurate and meets the specifications defined by the stakeholders.

Example-

• Scenario: Let's take an example of a calculator application that performs basic arithmetic operations such as addition, subtraction, multiplication, and division. In this case, the expected results can be calculated using a pre-defined set of test cases, and the actual results generated by the calculator application can be compared with the expected results.

For example, consider the following test case:

Test Case 1: Addition

Input: 2 + 2

Expected Output: 4

To perform Comparison Testing, we would execute the input (2 + 2) in the calculator application and compare the actual output generated by the system (i.e., 4) with the expected output. If the actual output matches the expected output, then we can conclude that the system is working correctly for this test case. However, if the actual output does not match the expected output, then there may be a defect in the system that needs to be fixed.

Similarly, we can perform Comparison Testing for other test cases involving different arithmetic operations such as subtraction, multiplication, and division, and compare the actual results generated by the system with the expected results to ensure that the system is working correctly.

In conclusion, Black Box Testing is an essential part of the software testing process, which involves testing the functionality and performance of software without knowing its internal structure. There are various techniques used in Black Box Testing, including Equivalence Partitioning, Boundary Value Analysis, State Transition Testing, Error Guessing, Graph-Based Testing, and Comparison Testing. Each technique has its advantages and disadvantages and should be used in combination to achieve effective testing results.