Black Box Testing: An In-depth Tutorial with Examples and Techniques

In this tutorial, we will familiarize ourselves with the types and techniques of Black-box Testing along with its process, advantages, disadvantages and some automation tools to test it other than manual testing.

We will also explore the differences between White Box Testing and Black Box Testing.

Most of us perform Black Box Testing every day! 

Whether we have learned or not, we all have performed Black box Testing many times in our day to day life!!

From the name itself we can probably understand that it implicates interacting with the system that you are testing as a mystery box. It means that you are not knowledgeable enough about the internal working of the system but you know how it should behave.

If we take an example to test our car or bike, we always drive it to make sure that it doesn’t behave in an unusual way. See? We have already done Black Box Testing.

List of “Black Box Test Techniques” Tutorials

Tutorial #1: What is Black Box Testing
Tutorial #2: What is White Box Testing
Tutorial #3: Functional Testing Simplified
Tutorial #4: What is Use Case Testing
Tutorial #5: Orthogonal Array Testing Technique

Techniques

Tutorial #6: Boundary Value Analysis and Equivalence Partitioning
Tutorial #7: Decision Table Testing
Tutorial #8: State Transition Testing
Tutorial #9: Error Guessing
Tutorial #10: Graph-Based Testing Methods

---

An In-depth Tutorial on Black Box Testing

What is Black Box Testing?

Black Box Testing is also known as behavioral, opaque-box, closed-box, specification-based or eye-to-eye testing.

It is a Software Testing method that analyzes the functionality of a software/application without knowing much about the internal structure/design of the item that is being tested and compares the input value with the output value.

The main focus of Black Box Testing is on the functionality of the system as a whole. The term ‘Behavioral Testing’ is also used for Black Box Testing.

Behavioral test design is slightly different from the black-box test design because the use of internal knowledge isn’t strictly forbidden, but it’s still discouraged. Each testing method has its own advantages and disadvantages. There are some bugs that cannot be found using black box or white box technique alone.

A majority of the applications are tested using the Black Box method. We need to cover the majority of test cases so that most of the bugs will get discovered by the Black-Box method.

This testing occurs throughout the Software Development and Testing Life Cycle i.e in Unit, Integration, System, Acceptance, and Regression Testing stages.

This can be either Functional or Non-Functional.

Types of Black Box Testing

Practically, there are several types of Black Box Testing that are possible, but if we consider a major variant of it then only the below mentioned are the two fundamental ones.

#1) Functional Testing

This testing type deals with the functional requirements or specifications of an application. Here, different actions or functions of the system are being tested by providing the input and comparing the actual output with the expected output.

For example, when we test a Dropdown list, we click on it and verify if it expands and all the expected values are showing in the list.

Few major types of Functional Testing are:

• Smoke Testing
• Sanity Testing
• Integration Testing
• System Testing
• Regression Testing
• User Acceptance Testing

=> Read More on Functional Testing

#2) Non-Functional Testing

Apart from the functionalities of the requirements, there are even several non-functional aspects that are required to be tested to improve the quality and performance of the application.

Few major types of Non-Functional Testing include:

• Usability Testing
• Load Testing
• Performance Testing
• Compatibility Testing
• Stress Testing
• Scalability Testing

=> Read More on Non-Functional Testing

---

Black Box Testing Tools

Black Box Testing tools are mainly record and playback tools. These tools are used for Regression Testing to check whether a new build has created any bugs in the previous working application functionality.

These record and playback tools record test cases in the form of scripts like TSL, VB script, Javascript, Perl, etc.

Black Box Testing Techniques

In order to systematically test a set of functions, it is necessary to design test cases. Testers can create test cases from the requirement specification document using the following Black Box Testing techniques:

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

Let’s understand each technique in detail.

#1) Equivalence Partitioning

This technique is also known as Equivalence Class Partitioning (ECP). In this technique, input values to the system or application are divided into different classes or groups based on its similarity in the outcome.

Hence, instead of using each and every input value, we can now use any one value from the group/class to test the outcome. This way, we can maintain test coverage while we can reduce the amount of rework and most importantly the time spent.

For Example:

As present in the above image, the “AGE” text field accepts only numbers from 18 to 60. There will be three sets of classes or groups.

Two invalid classes will be:

a) Less than or equal to 17.

b) Greater than or equal to 61.

A valid class will be anything between 18 and 60.

We have thus reduced the test cases to only 3 test cases based on the formed classes thereby covering all the possibilities. So, testing with any one value from each set of the class is sufficient to test the above scenario.

Recommended Read => What is Equivalence Partitioning?

#2) Boundary Value Analysis

The name itself defines that in this technique, we focus on the values at boundaries as it is found that many applications have a high amount of issues on the boundaries.

Boundary refers to values near the limit where the behavior of the system changes. In boundary value analysis, both valid and invalid inputs are being tested to verify the issues.

For Example:

If we want to test a field where values from 1 to 100 should be accepted, then we choose the boundary values: 1-1, 1, 1+1, 100-1, 100, and 100+1. Instead of using all the values from 1 to 100, we just use 0, 1, 2, 99, 100, and 101.

#3) Decision Table Testing

As the name itself suggests, wherever there are logical relationships like:

If
{
(Condition = True)
then action1 ;
}
else action2; /*(condition = False)*/

Then a tester will identify two outputs (action1 and action2) for two conditions (True and False). So based on the probable scenarios a Decision table is carved to prepare a set of test cases.

For Example:

Take an example of XYZ bank that provides an interest rate for the Male senior citizen as 10% and 9% for the rest of the people.

In this example condition, C1 has two values as true and false, C2 also has two values as true and false. The total number of possible combinations would then be four. This way we can derive test cases using a decision table.

#4) State Transition Testing

State Transition Testing is a technique that is used to test the different states of the system under test. The state of the system changes depending upon the conditions or events. The events trigger states which become scenarios and a tester needs to test them.

A systematic state transition diagram gives a clear view of the state changes but it is effective for simpler applications. More complex projects may lead to more complex transition diagrams thereby making it less effective.

For Example:

#5) Error Guessing

This is a classic example of Experience-Based Testing.

In this technique, the tester can use his/her experience about the application behavior and functionalities to guess the error-prone areas. Many defects can be found using error guessing where most of the developers usually make mistakes.

Few common mistakes that developers usually forget to handle:

• Divide by zero.
• Handling null values in text fields.
• Accepting the Submit button without any value.
• File upload without attachment.
• File upload with less than or more than the limit size.

#6) Graph-Based Testing Methods

Each and every application is a build-up of some objects. All such objects are identified and the graph is prepared. From this object graph, each object relationship is identified and test cases are written accordingly to discover the errors.

#7) Comparison Testing

In this method, different independent versions of the same software are used to compare to each other for testing.

How do I do Step-wise?

In general, when a systematic process is followed to test a project/application then quality is maintained and is useful in the long run for further rounds of testing.

• The foremost step is to understand the requirement specification of an application. Properly documented SRS (Software Requirement Specification) should be in place.
• Using the above mentioned Black Box Testing techniques such as Boundary Value Analysis, Equivalence partitioning etc, sets of valid and invalid inputs are identified with their desired outputs and test cases are designed based on that.
• The designed test cases are executed to check if they Pass or Fail by verifying the actual results with the expected results.
• Failed test cases are raised as Defects/Bugs and addressed to the development team to get it Fixed.
• Further, based on the defects being fixed, the tester retests the defects to verify if they are recurring or not.

Advantages and Disadvantages

Advantages

• The tester does not need to have a technical background. It is important to test by being in the user’s shoes and think from the user’s point of view.
• Testing can start once the development of the project/application is done. Both the testers and developers work independently without interfering in each other’s space.
• It is more effective for large and complex applications.
• Defects and inconsistencies can be identified in the early stages of testing.

Disadvantages

• Without any technical or programming knowledge, there are chances of ignoring possible conditions of the scenario to be tested.
• In a stipulated time there is a possibility of testing less and skipping all possible inputs and their output testing.
• Complete Test Coverage is not possible for large and complex projects.

Difference Between White Box Testing and Black Box Testing

Given below are some of the differences between the two:

Conclusion

These are some of the basic points regarding Black box testing and the overview of its techniques and methods.

As it is not possible to test everything with human involvement with 100 percent accuracy, if the above-mentioned techniques and methods are used effectively, then it will definitely improve the quality of the system.

To conclude, this is a very helpful method to verify the functionality of the system and identify most of the defects.

Hope you would have gained an in-depth knowledge of Black Box Testing techniques from this informative tutorial.