Introduction


What comes to your mind when you hear the term Black box, specifically concerning testing? Well, it is something that is not very common to listen to but remains an essential form of software testing. So, it is a software testing technique to examine the functioning of software from an external outlook without digging deeper into its code. The best thing about Black box testing is that it can be applied to all levels of testing ( Unit, integration, system, and acceptance). Anybody with minimum or no coding language can perform Black box testing of a software product, software testers with no coding language can also do it.

What is Black Box Testing? 

In a black box, we cannot look through the box to know what is inside; we only know from the outside that it is a black-colored box. Similarly, in the software testing field, Black Box testing is a testing technique to examine the application under test without stressing its design and internal coding structure. It is performed to inspect the behavior of the software from the outside. Hence, it is also called behavioral testing, i.e., how your software behaves under different situations without looking at the details of the code. In some or the other way, we all have tried Black Box testing in our lives. For example, while pressing the start button of a bike, we expect it to start without getting into its inner working mechanism.

In other words, it focuses on the functionality of the software without any need for coding knowledge. It includes software testing from the customer’s point of view, the user interface of the software. It examines the product-customer relationship, performed to find out the external factors that impact the success or the failure of the software. Black Box testing is done at the final stages of the testing process to examine the functional aspects of the software. It focuses only on the input and the output of the application.

black box testing



Black box testing helps testers identify the following issues:

– Missing functions of the software

– Errors occurring while using the application interface

– Errors while accessing the database

– Errors occurring during the start and end of a particular function

 – Issues in application performance and behavior

Black box testing tests the application, keeping the end-user in mind. It checks the usability, functionality, and the performance of the application as a complete system.

White box vs. Black box testing

White box testing, in contrast, is a testing methodology purely focused on the working of the internal code structure of the software. It requires an in-depth knowledge of coding to understand the way the software is built. Black box testing is not an alternative for White box testing. It is complementary to it. For example, if you are making a transaction on the website and testing if any faults occur while transacting, it is identified with the help of Black box testing. Whereas, if you look into the source code of the same website to check the functioning of a particular form, understand the variables, restrictions based on core coding knowledge, it is called White box testing. In other words, white box testing provides an internal perspective of the overall system, it checks the design and internal structure of an application using supreme programming skills.

Examples of Black box testing

Let’s have a look at a couple of examples of Black box testing to have a better understanding of this testing methodology.

Example 1: Testing if the word processor is working as expected. One scenario is to examine if the user can create a new file, save, open, or delete the existing file. Another scenario could be testing the functioning of editing tools like cut, copy, select, change font size/color of the document, etc.

Example 2: Testing Login Function of a website login screen. With the help of Black box testing, the tester will test if using a username and password (input) allows one to login seamlessly to the system (output). Here, the tester will not get into the function of the code behind it; he will just check the validity of the input given and the outcome received. If the user feeds a wrong password and does not get any error message, black box testers detect this and send it to the coders for resolution.

There are different approaches to execute Black box testing, like:

Manually: By testing user data and error messages, check the UI of the application as a user.

Automatic: It records the user interaction with the software to figure out errors

Documentation: A type of manual approach in which the tester documents the functions that the software should perform without focusing on how it should perform them.

Types of Black box testing

With its growing scope, Black box testing has many types, out of which the prominent and most preferred ones are:

Functional Testing: It is the most commonly used type of black box testing in which the tester focuses on the core functionality, operations, and specifications of the software. Testers perform it by feeding input to the application for getting the desired output. It is usually performed before non-functional testing. Various types of functional testing are Smoke, Unit, Integration, User acceptance testing, etc., and can be performed either in a manual or automated way.

Non-Functional Testing: This type of Black box testing focuses on aspects other than functionality of the software like usability, reliability, scalability, and performance. Any issue related to these aspects can critically impact the user experience. Hence it is necessary to maintain the quality of the product. Various types of non-functional testing are load, performance, stress, compliance testing, etc.

Regression Testing: It is carried out after code fixes/changes or system upgrades to ensure any code modification should not impact the existing functionalities of the software. It is an essential part of the SDLC; any software must go through regression testing to handle unseen implications.

Techniques of Black box testing

We know how impactful and beneficial Black box testing can be to the organization in improving the quality of its software application. There are many techniques of Black box testing available for fulfilling software testing requirements. Let’s have a look at the popular ones to include in the test strategy.

  1. Equivalence Partitioning
    In this type of Black box testing technique, the inputs that behave homogeneously or yield similar outcomes are divided and grouped under one category. One input value from each group is picked and tested. For every group, one representative value is selected and tested. Testing each value in the group would be time-consuming. In this technique, only the representative value is tested from each group, making it easier to test many inputs at once, maintaining test coverage, and reducing rework.
  2. Boundary Value Analysis
    It is a popular black box testing technique that works on similar lines of equivalence testing. However, instead of testing the representative value from each group, this technique tests the boundary value of each input group (including both valid and invalid inputs). It is observed that applications face problems near the boundary, which means that the limit after which the system starts behaving differently.
  3. Decision Table Testing

    This technique is appropriate in conditions where the functionalities have logical input between them, like if/else conditions. Here different input combinations are considered. We use conditions (inputs) and actions (outputs) to examine system behavior using decision tables.

  4. State Transition Testing

    In this technique, the inputs/outputs and system states are considered in the entire testing phase. It tests the software application for a sequence of transitions of test inputs. It checks the system behavior changes depending upon what events have occurred/ or what input value is given. Events set off states which become scenarios that the testers test. For example: When a user enters a wrong password thrice, all three inputs will be sent to the login page. The third attempt will produce an error message for the user. This method considers all three system states and passes only the right state sequence.

  5. Graph-based testing

    A graph is prepared for the objects that the application consists of. Then based on this object graph, the relationship between each object is figured out, and a test is written to discover errors. It visualizes the flow and correlation of inputs and outputs.
  6. Error guessing technique:

    This testing technique is entirely experience-based. Here, the tester guesses the erroneous aspects (input/output) of the application. The judgment is solely based on his previous experience with the software behavior, functionalities, and impacts on end-user experience.

Apart from the above-stated techniques of black box testing, there are a few more, such as all pair testing and orthogonal array testing, comparison testing, etc.

Conclusion

To ensure that the software quality is maintained and you do not lose customers because of a bad user-experience, your application should go through stern supervision using suitable testing techniques. Black box testing is the easiest and fastest solution to investigate the software functionalities without any coding knowledge. The debate on white box vs. black box testing is an ever-prevailing discussion, where both stand out as winners. Whether you want White box testing or Black box testing depends upon how deeper you want to get into the software structure under test. If you want to test the functionalities with an end-user perspective, Black box testing fits the bill. And, if you wish to direct your testing efforts towards how the software is built, its coding structure, and design, then white box testing works well. However, both aim to improve the software quality in their own different ways. There are a lot of black box testing techniques discussed above. A tester can combine different techniques to reap the benefits of black box testing. Whatever testing method you use, the ultimate aim of your testing strategy should be to minimize errors and the risks of app failure and maximize software quality and user experience.

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