Introduction to Black Box Testing

Black Box Testing is a software testing method wherein the internal structure or design, or implementation of the item that needs to be tested is unknown to the tester. Black box testing is a software testing technique that focuses on the analysis of software functionality versus internal system mechanisms. Black box testing was developed as a method of analyzing client requirements, specifications, and high-level design strategies. A black box software tester would select valid and invalid input set and code execution conditions and checks for valid output responses. Black box testing is also referred to as functional testing or closed-box testing.

Software testing is the procedure of evaluating a system with the intent of finding bugs. It is performed to check if the system satisfies its specified requirements. Testing measures the overall quality of the system in terms of its correctness, completeness, usability, performance, and other functional and non-functional attributes.

For example, A search engine of an application. In a search engine, a user would enter text in the browser’s search bar. The search engine would then locate and retrieves related user data output. What is going behind the scenes is unknown to the user. Thus, internal implementation is of no understanding of him.

Black box testing advantages include:

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Simplicity: Facilitates testing of high-level designs and complex applications.
Conserves resources: Testers focus on software functionality.
Test cases: Focusing on software functionality to facilitate quick test case development.
Provides flexibility: Specific programming knowledge is not required.

Example:

The tester would test the web pages, that is, through clicks and keystrokes by using a browser by providing inputs and without the knowledge of the internal structures, thus verifying the outputs against the expected results.

Tools used for Black Box Testing

Black box testing tools basically depend on what type of black-box testing you are implementing.

Functional/ Regression Tests can be done through QTP or Selenium.
Non-Functional Tests can be done through LoadRunner or Jmeter.

Levels:

In Black Box Testing, the following levels are for software testing:

Integration Testing
System Testing
Acceptance Testing

As the level is higher, the box would be bigger and more complex, and also, more black-box testing comes into the picture.

Understanding Black Box Testing

Black box testing can be defined as a testing technique wherein Application Under Test (AUT)’s functionality is tested but overlooking the structure of the internal code, details of implementation, and any knowledge of the internal paths of the software.

Black box testing is regarding all software specifications and requirements. Black Box Testing just focuses upon inputs and output of the software system and not bothering at all regarding internal knowledge of the software.

How does Black Box Testing make Working so Easy?

There is the Software Testing Life Cycle, that is, STLC, which is of Black box testing, which is relative to each stage of the Software Development Life Cycle.

In the initial or first stage of STLC, the requirements of the product are collected. This is known as the Requirement Gathering phase.
The phase that follows is Test Planning and Test Analysis phase. The deliverables of this phase generally are types of testing to be done as per the project and a test plan to determine risks and mitigation to these risks.
The third phase is the designing phase, in which test cases, test scripts are prepared with the help of the software requirement documents or business requirement documents.
The last stage is known as the Test Execution phase. As the name implies, in this stage, all the test cases or scripts are executed. All the bugs found are reported, fixed, and retested.

What can you do with Black Box Testing?

Some of the prominent Test Strategies used in Black Box Testing are given below :

Equivalence Class Testing
Boundary Value Testing
Decision Table Testing
Cause-Effect Testing
Requirement Based Testing
Compatibility Testing

1. Equivalence Class Testing

This type of testing is preferred as it helps in minimizing the test cases to a level where the chances of requirement coverage are to an optimum level.

This is done in the following two steps:

Identifying and partitioning into equivalence classes: At first, the input data is partitioned into a minimum of two sets – the first set contains a list of valid input values, and the second set contains the list of invalid input values. For example, if there is an age box that can contain age in the range of 20-40, then valid input values can be 21, 25, 30, 39, etc. and invalid input values can be any value less than 20 or greater than 40 like 10,15,45,55, etc.
Creating test cases – A unique identification number is assigned to each valid input class, and invalid input class, and then test cases are written with an intention to cover the two sets of input classes.

2. Boundary Value Testing

Boundary value testing basically focuses on boundaries values. It evaluates whether or not a certain range of values would be acceptable by the system or not. Boundary Value testing is useful in reducing/minimizing the number of test cases. Boundary Value testing is most suitable for the systems where input lies within certain ranges.

3. Decision Table Testing

A decision table demonstrates causes and their simultaneous effects in the form of a matrix. In decision table testing, there exists a unique combination in each column.

4. Cause-effect Graphing

Cause-effect Graphing develops a relationship between causes (logical inputs) with corresponding effects (Actions). They are represented with the help of Boolean graphs.

The steps to be followed are as follows :

Identification of inputs and outputs.
Development of cause-effect graph.
Transformation of the graph into the decision table.
Conversion of decision table rules into test cases.

5. Requirement Based Testing

This type of testing includes checking if the requirements mentioned in the SRS or Software Requirement Specification are valid or not.

6. Compatibility Testing

In order to deliver functionality, both the products and infrastructure depend upon the result of the test case executions. Irrespective of the changes made in the infrastructure parameters, the product is still expected to work properly.

Some of the parameters generally affecting the compatibility of software are listed below:

Pentium 3 or Pentium 4 processors and the number of processors used.
32 bit or 64-bit architecture.
Database servers or any other back end components.
Type of Operating System (Windows, Linux, etc.)

Working with Black Box Testing

Following are the basic steps needed to perform Black Box Testing.

Firstly, the specifications and requirements of the system are dealt with.
Secondly, the tester would choose logical inputs, that is, positive test scenarios, in order to check out whether SUT has processed them correctly or not. In addition, invalid inputs also, that is, the negative test scenario, is also chosen to check that the SUT can detect them.
Thirdly, testers would then determine expected outputs for all of the valid inputs.
Fourthly, the software tester creates test cases with those selected and valid inputs.
Fifthly, created test cases are executed.
Sixthly, software testers distinguish between the actual outputs with the expected outputs and check if they are the same.
Lastly, if any are found, they are fixed and re-tested.

Advantages and Disadvantages

Below are the advantages and disadvantages mentioned:

Advantages:

Black box tests are always executed from a user’s point of view since they would help in exposing discrepancies significantly.
Black box testers also do not need to know any programming languages.
Black-box testers do not need to know how the software has been implemented.
Test cases related to a black box are designed by testers as soon as the specifications are in the completed stage.

Disadvantages:

Since no technical or programming knowledge is needed, there might be instances to ignore all valid and possible conditions of the scenario that has to be tested.
There are possibilities of less testing and ignorance of each and every possible input and their output testing because of time constraints (stipulated time).
The complete and finished test Coverage is often not possible for complex and large projects.

Why should we use Black Box Testing?

Tools of Black box testing are basically record and playback ones. These tools record the test cases in the form of scripts like TSL, JavaScript, VB script, etc. All of these tools are basically used for regression testing in order to check whether the provided new build has made any defect in already fine working application functionality.

Scope

The prominent and most important types of Black Box Testing are the following ones:

Functional testing: This type of black-box testing is all regarding the functional requirements of the system, and it is executed by software testers.
Non-functional testing: This type of black-box testing is not regarding testing of the particular functionality, but all regarding non-functional requirements such as performance, usability, scalability and much more.
Regression testing: Regression Testing is executed after a code is fixed; any code upgrades or any other maintenance of the system is done to verify whether the new code has not affected the existing functionality.

Differences

Black Box Testing is the software testing technique wherein the internal structure or design, or implementation of the product that is being tested is unknown to the tester. White Box Testing is a software testing technique wherein the internal structure or design, or implementation of the product that is being tested is known to a tester.

Black Box Testing	White Box Testing
Black box testing is wherein the internal structure, or the program, or the code is unknown.	White box testing is wherein the tester has knowledge about the internal structure of software.
It is usually done by software testers.	It is usually done by software developers.
Here, absolutely no knowledge of implementation is required.	Here, Knowledge of implementation is required.
It can be also be called outer/external software testing.	It can also be called as inner/internal software testing.
Black box testing is the functional test of the software.	White box testing is the structural test of the software.
This testing can be initiated on the basis of the requirement specifications document.	This type of testing of software is started after a detailed design document.
Here no knowledge of programming language is required.	Here it is compulsory to have knowledge of at least one programming language.
It is basically the behavior testing of the software.	It is the basic logic testing of the software.
It is mostly applicable to the higher levels of testing.	It is mostly applicable to the lower levels of testing.
It is also called behavioral testing.	It is also called as clear or glass box testing.
Black box testing is less time-consuming than White Box testing.	White box testing is more time-consuming than Black box testing.
It is not appropriate for algorithm testing.	White box testing is appropriate for algorithm testing.
It can be accomplished by trial and error methods.	The inner or internal boundaries of data, along with its domain, can be tested thoroughly.
For instance: Searching something on google with the help of keywords.	For instance: Using inputs to check and verify for loops.
Types Functional Testing Non-functional Testing Regression Testing	Types Path Testing Loop Testing Condition Testing

Conclusion

All the topics discussed are basic as well as advanced topics related to Black box testing and the gist of all of its techniques and methods. Since it is hardly possible to test each and everything along with human involvement and that too with 100 percent accuracy but if the already specified methods are used very effectively, it will, without any doubt, enhance the quality of the system. Therefore in order to end, it is a seriously very effective method to identify the defects as well as verify the functionality of the system.

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