Black Box Testing

Application Software
27 Sep 2022
What is Black Box Testing?
Advantages of Black Box Testing
Black Box Testing Process
Types of Black Box Testing
Black Box Testing Techniques

What is Black Box Testing?

A type of software testing in which an application software is tested by software testers to verify if it works for end-users as intended, without being concerned about its inner workings.
  • “The software tester need not have prior knowledge on the internal code structure, implementation details of each functionalities and internal paths or flow of the software application to be tested.”
  • Black Box Testing mainly focuses on the outputs generated for the corresponding inputs submitted to the different functionalities of the software application to be tested and it is entirely based on software requirements and specifications.

Advantages of Black Box Testing

Major advantages of Black Box testing are,
Black box testing is performed from an end-user’s perspective. So the software tester does not need to have technical knowledge or programming skills to implement it.
Black Box testing can be executed by crowdsourced or outsourced testers.
Test cases and test scenarios can be created immediately after the software requirements and specifications are obtained.
Both software testers and software developers work independently without interfering in each other’s space which reduces unwanted bias.
Black Box testing helps in identifying ambiguity and contradictions in the functional specifications of the application/project.
It is more effective for large and complex applications.
Since black box testing is performed from a common user’s point of view, it has a higher possibility of satisfying customer expectations and needs.

Black Box Testing Process

The sequence of steps followed commonly to carry out Black Box Testing are briefed below.
1.
Initially, the requirements and specifications of the application software to be tested are examined. Properly documented SRS (Software Requirement Specification) of the application/project should be available.
2.
Valid inputs (positive test scenario) are chosen by the software tester to be used for the test cases that checks whether the application under test processes them correctly. Also, some invalid inputs (negative test scenario) are chosen to be used for the test cases that verifies whether the application is able to detect them.
3.
The next step is to identify the set of test scenarios for which test cases are to be framed.
4.
Software tester constructs test cases with the chosen inputs for the identified test scenarios.
5.
Software Tester determines expected outputs for the chosen inputs for each test case.
6.
The test cases are executed.
7.
Software tester compares the actual outputs with the expected outputs.
8.
Failed test cases are marked as Defects/Bugs and addressed to the development team to get them Fixed.
9.
Finally, the software tester retests the defects once they are rectified to confirm that they are not recurring.

Types of Black Box Testing

The 3 most prominent types of black box testing are,
1. Functional Testing: - Black box testing can be used to test the functions or features of the application software under test. It covers the functional requirements and specifications of a software program.
  • Functional testing is performed by providing a certain input to a function or a feature and verifying if the output from it meets the conditions specified in the software requirements and specifications.
  • Various types of functional testing are Smoke Testing, Unit Testing, Integration Testing, User acceptance testing, etc., and can be performed either manually or by automation.
2. Non-Functional Testing: - Black box testing can also be used to test non-functional requirements of an application software such as performance, scalability, security and usability.
  • Non-functional testing is important for maintaining and improving the quality of an application software as real end-users may experience critical issues while using the application that are not related to its functionality.
  • Various types of non-functional testing include Load Testing, Performance Testing, Stress Testing, Usability Testing, Scalability Testing, etc.
3. Regression Testing: - Regression Testing is normally done after code corrections, upgrades or any other maintenance activities on the application software to confirm that the new code modifications haven’t adversely affected the existing functionalities or features of the application software.
“Any application software must go through regression testing to rule out the possibilities of unseen implications after its modification.”

Black Box Testing Techniques

Following are the prominent test case design strategies commonly applied for Black Box Testing.
1. Boundary Value Analysis: -
  • Used to identify the bugs that arise due to the lower and upper limits of data applied as inputs.
  • The boundaries for input values are determined initially and then values that are at the boundaries are selected as test data. Also, values that are near to inside/outside of boundaries are selected.
  • Test the application software with test cases that have these extreme values of test data as inputs. This increases the efficiency of testing as the probability of finding errors increases at these boundaries.
2. Equivalence Partitioning :-
  • The test data inputs are partitioned into groups based on their similarity in the outcome and only one test data input from every group is used for testing to examine the results.
  • This testing assumes that a test case will run identically for equivalent inputs from the same group. So, only one input value from each group is picked and tested.
3. Decision Table Testing :-
  • A decision table has a different set of input conditions and their corresponding expected outcomes on each row.
  • Rules, which are a combination of conditions, are identified initially by software testers.
  • The outcome of each rule is identified further to design a test case for each rule.
  • This technique works well when there are multiple input combinations and possibilities.
4. State Transition Testing :-
  • If a state transition action is identified, software testers can design test cases that examine this transition of states. An example- for a system that locks the account after five failed login attempts, a test case can check what happens at the sixth login attempt.
  • This testing technique applies to those types of applications that provide a specific number of attempts to access a functionality.
5. Error Guessing :-
  • Involves testing for common errors made by software developers while developing similar software applications.
  • The software testers can make use of the experiences they have gained by testing similar applications to guess the error-prone areas.
  • Knowing possible errors or error-prone areas, the software testers can identify high risk code sections that are to be tested thoroughly.
6. Cause Effect Graph :-
  • A software testing technique in which the causes (input conditions) and effects (output conditions) are identified initially and a Cause-Effect Graph that depicts the link between the causes (inputs) and the effects (output) is produced. Test cases are generated based on this cause-effect graph.
  • This testing utilizes different combinations of inputs and outputs. The coverage of cause-effect graphs is based on the percentage of combinations of inputs tested out of the total possible combinations.

Conclusion

  • Black box testing mitigates the risk of software failures at the user’s end as tests are done from a user’s point of view. If done correctly, it is an excellent way to ensure that the system works in line with end-users expectations without worrying about the system's inner workings.
  • Black box testing is the easiest and fastest solution to investigate the software functionalities without any coding knowledge.
  • It helps in exposing discrepancies present in the software requirement specifications prepared prior to the development of the application software thus facilitating an excellent finish for the application.