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Black Box Testing

What is Black Box Testing? A Complete Guide Including Types and Techniques

The name of black-box testing is quite obvious that implicates that a system you are interacting with is a mystery box. It means you will be totally blank about the internal working of the system. However, you will be familiar with the behavior of the system.


Black box testing examples are everywhere. So you most often keep doing black-box testing without knowing it. For example, to test your bike or car, what do you do? You most probably drive to make sure that the behavior is either usual or not. Is that so? If yes, it means you have already done black-box testing.


What is black box testing?


It is a most popular testing technique which is used to test the functionality of a system or software without looking at the internal working methodology or coding structure. Furthermore, this testing doesn’t concern with the knowledge of internal paths and implementations details. The system that is being tested is known as the Application Under Test (AUT).


Black box testing is also known as closed-box, behavioral or opaque-box testing. Furthermore, it is also known as eye-to-eye or specification-based testing. This process of entire black box testing is based on software requirements and specifications. The main point of focus is only inputs and output of the system in this testing. This testing doesn’t bother to check how the system processes the inputs to give output.


You might be thinking that which type of system you can test with black-box testing. You can perform black-box testing on any software system. For example, different operating systems, databases, websites and your own custom software and applications. A scenario can be changed but working methodology will be the same. Let’s learn the complete methodology of black-box testing.


How to do black-box testing?


Here are the fundamental steps to perform black-box testing:

  • Black box testing is all about the requirements and specification of the system. So at the initial stage, both are examined.
  • There are two different test scenario. First, a positive test scenario includes a set of valid input values. Second, a negative test scenario which contains a set of invalid input values. Valid values are given to verify the appropriate working of the system. Different invalid values are selected to verify that the SUT is capable to detect them and how a system behaves on wrong inputs.
  • After creating different test scenarios, the tester determines the correct value on a specific input.
  • After developing both test scenarios, tester starts execution of all test cases.
  • After getting the output, tester compares both the resulted value and expected actual value.
  • If there is any flaw, it will be fixed and re-test again.


Different types of black-box testing


There are numerous types of black-box testing according to different experts. However, here are the most prominent types are as follows:


1. Functional testing


It is the most popular type of black-box testing which deals with the functional requirements and specifications of a system. An application contains several functions or activities that are tested by giving the different tested values and compare the output with the expected results.


For testing a dropdown list, you perform functional testing. You just click on it to verify that either it is expending or not? Furthermore, either it is showing the complete list of values or not? Functional testing has been divided into further types. Here are a few most prominent types of functional testing:


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


2. Non-Functional testing


There are numerous non-functional aspects apart from the functional requirements that are really important to be tested which enhance the performance and quality of the application.


You will have to check how much your application is secure? What will happen if too many users sign in concurrently? Is application capable to recover from disastrous situations? You answer all these questions by performing non-functional testing.

Non-functional testing is divided into some other major categories. Here are the few most popular types of non-functional testing:


  • Load Testing
  • Scalability Testing
  • Compatibility testing
  • Performance Testing
  • Stress Testing


3. Regression Testing


Most of the people don’t consider it a specific type of black-box testing. They consider it a type of functional testing. Regression testing is performed after fixing, modifying the code or other system maintenance activity. It is done to check that either system is working properly after modifying it or not.


Different tools used for black-box testing


There are several tools available on the internet that are extremely helpful in black-box testing. Before picking a specific tool, your mind should be clear that which type of testing you are going to perform? It is because black box testing tools mostly depends on the type of testing.


  1. For Functional testing, QTP is one of the most preeminent tools. Furthermore, Selenium is another most remarkable tool for functional testing. Both of these tools are widely used for regression testing as well.
  2. For non-functional testing, there are two most dominant tools: LoadRunner and Jmeter. Picking tools depends totally on your own choice. Some people like one functionality and others like some others. So it is up to you, which tool you are comfortable with.


Black box testing techniques


  1. It is an essential step to designing different test cases for systematically testing a set of functions. A tester can adopt following black box testing techniques to create different test cases:
  2. Equivalence Partitioning: Sometimes this technique is called Equivalence Class Partitioning (ECP). In this technique, input values are divided into different groups and instead of using numerous input values, only one value of that group is enough for testing. On the other hand, you can divide the application into different classes based on similarity and test just one class instead of all. This technique really reduces a lot of rework and the time as well.
  3. Boundary value testing: Name is quite obvious. In this technique, the focus point is to test the boundaries values. At the boundary, the behavior of the application is changed. For example, if a system accepts inputs from 1 to 100, 1 and 100 will be boundaries values. So you will have to test 1, 1+1, 100, 100-1, etc. values to test the system.
  4. Decision table testing: In this technique, a logical relationship is involved as the name suggests. Tester identifies two expected outputs for two separate conditions.
  5. State Transition Testing: This technique is used to test the different states of the application under test. These states keep on changing depending upon the events and conditions. An event initiates different states that further create several scenarios and tester has to test them. To have a clear view of the state changes, systematic state transition diagrams are used.
  6. Error Guessing: Testers can use their own experience to guess the different error-prone areas about the functionalities and behavior of the application. Here are a few most common mistakes that coder most often forget to handle:
  • Divide a number by zero.
  • To handle null values in some input fields.
  • File upload even without attachment.
  • The form is submitted without any value.


There are a few other most common types of testing such as graph-based and comparison testing – which deals with the different versions of the same software. So you can use all these testing methods to mitigate the risks.


Black box testing and white box testing


Most people mix black box testing (BBT) with white box testing (WBT). Both are totally different things. In this guide, we have explained the most common differences between both testing techniques for the interest of the user. Here are a few common differences between both:


  • BBT is used to validate overall functional requirements but WBT is deal with the internal structure and working of code.
  • BBT is most often done by testers but WBT is done by developers.
  • In BBT, programming knowledge is not required but for WBT it is mandatory.
  • BBT is not preferred for algorithms testing but WPT is the best for algorithms testing.
  • BBT takes less time to perform testing but WPT is much more time-consuming.
  • To search something on Google is an example of BBT and to give an input to test the loops working is an example of WBT.


Black box testing and software development life cycle (SDLC)


BBT is comprised of its own lifecycle that is known as SDLC. This lifecycle covers almost every step of testing.

  1. Requirements: This is the first step which is used to collect complete requirements of the software. In this stage, different software testers take part.
  2. Test planning and analysis: In this step, a testing plan is created to figure out the different possible risks in the project. For example, a starting point to test software and different testing strategies come under discussion.
  3. Design: There are different test cases and scripts are created based on software requirement documents.
  4. Test Execution: In this stage, your complete test plan is deployed. If any bugs emerge, fix that and again re-tested.