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

In this tutorial, using my industrial experience in software testing, let’s familiarize 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 learn about the differences between white box testing and black box testing.

Almost all of us perform black box testing every day! 

Whether we have learned or not, we all have and performed black box testing many times in our day to day life!!

From the name itself you 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 already have done black box testing.

What You Will Learn:

What is Black Box Testing?

Black box testing, which is also known as behavioral, opaque-box, closed-box, specification-based or eye-to-eye testing, is a Software Testing method that analyses 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 in 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 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 the only black box or only white box technique. Majority of the applications are tested by black box method. We need to cover the majority of test cases so that most of the bugs will get discovered by a 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 both 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 the major variant of it then below mentioned are the two fundamental ones.

#1) Functional Testing

This 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 that it expands and all the expected values are showing in the list.

Few major types of Functional Testing are:

=> Read More on Functional Testing.

#2) Non-Functional Testing

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

Few major types of Non-functional testing include:

=> Read More on Non-Functional Testing.

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.

Let us 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. In this way, we can maintain the test coverage while we can reduce a lot of rework and most importantly the time spent.

For Example:

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

Two invalid classes will be:

a) Less than or equal to 17.

b) Greater than or equal to 61.

One valid class will be anything between 18 to 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:

From the name itself, we can understand 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 means the values near the limit where the behavior of the system changes. In boundary value analysis both the valid inputs 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 that, 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 interest rate for the Male senior citizen as 10% and for rest of the people 9%.

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

#6) Graph-Based Testing Methods:

Each and every application is 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:

Different independent versions of same software are used to compare to each other for testing in this method.

How to do Step-wise?

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

Advantages and Disadvantages

Advantages:

Disadvantages:

Difference between White Box Testing and Black Box Testing

Given below are few differences between the both:

Black Box Testing White Box Testing

It is a testing method without having knowledge about the actual code or internal structure of the applicationIt is a testing method having knowledge about the actual code and internal structure of the application
It is a testing method having knowledge about the actual code and internal structure of the applicationThis type of testing is performed at a lower level of testing such as Unit Testing, Integration Testing
It concentrates on the functionality of the system under testIt concentrates on the actual code – program and its syntax's
Black box testing requires Requirement specification to testWhite Box testing requires Design documents with data flow diagrams, flowcharts etc.
Black box testing is done by the testersWhite box testing is done by Developers or testers with programming knowledge.

Tools

Black box testing tools are mainly record and playback tools. These tools are used for regression testing that to check whether new build has created any bug in previous working application functionality. These record and playback tools record test cases in the form of some scripts like TSL, VB script, Javascript, Perl etc.

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 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 technique.