A Guide On Black Box Testing (With Types And Strategies)

By Indeed Editorial Team

Published 25 April 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

Testing is a crucial part of the software development lifecycle, and it helps companies fix errors and improve the quality of their products before launching them. Professionals use black box tests to evaluate the specifications and functionalities of software. If you are interested in becoming a software tester, understanding the features and importance of black box tests can help you succeed as one. In this article, we discuss black box testing, analyse its characteristics, types, advantages, explore the testing strategies and learn the steps of a black box test.

What Is Black Box Testing?

Black box testing, also known as behavioural testing, involves testing a product, software or system with no prior knowledge of its internal architecture. Testers simulate user activity to evaluate user experience and identify if the system performs as expected. It mainly focuses on the input and output, emphasising software requirements and specifications. It is a powerful testing technique that evaluates the system from end to end.

Features of black box are:

  • Black box tests evaluate the entire system as a whole.

  • It also evaluates relevant subsystems like the UI/UX, database dependencies, web servers, application servers and other integrated systems.

  • It checks the response time, usability, scalability and reliability of the system.

  • It ensures that the system delivers the expected outputs for various inputs.

  • It tests both the functional and non-functional requirements of a system.

  • It does not require access to the coding, internal architecture or design of the system.

  • They can work independently from developers, ensuring user-centric and unbiased testing.

Related: Guide To Software Testing Careers (Skills And Salary)

Types Of Black Box Tests

Following are the three major categories of black box testing:

Functional testing

A functional black box test evaluates the specific features and functions of the software or product. For example, testing a website's login feature falls under functional testing. The test checks if the user can log into the site using correct user credentials. Functional tests usually focus on the most critical aspects of software, the integration between essential components and the system as a whole. Examples of functional tests include:

  • Unit-testing

  • Sanity testing

  • Smoke testing

  • Integration testing

  • System testing

  • User acceptance testing

Non-functional testing

Unlike a functional test that checks if the software can perform a specific feature or action, a non-functional test checks how the software performs a particular activity. These tests help measure the non-functional requirements like performance, usability and scalability. Examples of non-functional tests include:

  • Evaluating the performance of a system under average and peak loads

  • Checking the compatibility of software, app or system across various devices, operating systems and browsers

  • Monitoring the performance of the system against common security threats and vulnerabilities

Regression testing

Regression testing checks if the new version of the software exhibits a regression (or degradation) in performance and capabilities from one version to the next. Software testers use regression testing whenever the system has received an upgrade, a code fix or during the release of a new version. Testers use this methodology to evaluate both the functional and non-functional aspects of the software. Examples of regression tests include:

  • Checking if a specific software feature works as expected in the new version

  • Evaluating if an operation that performs well in the earlier version performs as expected in the latest version

Related: What Does A Performance Tester Do? (Skills And Salary)

Black Box Test Strategies

Here are some of the standard techniques used while designing black box test use cases:

Equivalence partitioning

This strategy minimises the number of possible test cases while ensuring adequate coverage of all possible inputs. Testers divide the inputs into groups or partitions. The tester checks only one value from each group, assuming that if one value in a group works, the rest are also likely to work. The input values are usually numbers, boolean conditions or a set of values. For example, if a field accepts integers from one to 20, the test can have three use cases, including a number between one and 20 and two invalid inputs like -10 and 100.

Boundary value testing

This strategy focuses only on testing the values at boundaries. Boundary value testing helps in reducing the number of test cases and is best suited for systems where the input falls within a specific range. For example, a company runs an offer targeted at customers aged between 18 and 40. Boundary value testing checks the values at the boundaries 18 and 40, along with two outliers 17 and 41, to see if the system accepts or rejects the values accordingly.

Decision table testing

It is a testing technique where the tester evaluates system behaviour for various input combinations. It is a systematic approach and tabulates cause and effect in a matrix form, with each row having a unique combination. This strategy involves multiple test cases where testers will check each condition to ensure outputs are accurate. It is best suited for systems with various input combinations and multiple-output possibilities.

Here is an example of a decision table for a login screen. The various possible use cases are:

  • Case 1: Username and password are both wrong.

  • Case 2: The username is correct, but the password is wrong.

  • Case 3: The username is incorrect, but the password is correct.

  • Case 4: Both username and password are correct.

State transition testing

This testing strategy is for systems with a state transition based on the response. For example, a user wants to log into an application. If the user enters the password wrong, then the system locks the user out after a particular number of attempts. Here, the system transitions from an available to a locked state. This testing strategy checks whether the system transitions accurately from one state to another based on the inputs.

Error guessing

This testing strategy looks for common mistakes that developers are likely to make when designing the system. For example, testers can check if the developer has defined how to handle null values in a field that accepts numeric characters. It helps identify various faults that other systematic black box tests may fail to detect. The efficiency of this testing strategy depends on the tester's prior experience and their ability to guess possible developer mistakes and oversight.

Penetration testing

Also known as pen testing, this is a method to discover and fix security vulnerabilities in a system. The tester attempts to imitate the behaviour of malicious players who attack an application from the outside. By creating probable attack and hack scenarios, the tester tries to understand the system's behaviour in case of an actual attack. This testing method can help rectify all attack vectors before the launch of the software.

Related: How To Become A Software Tester: A Step-by-Step Guide

Advantages Of Black Box Tests

Here are the top benefits of running black box tests:

  • Good choice for functional testing as it evaluates the behavioural aspects of software or a system

  • Easy to create test cases

  • Helps in quick implementation

  • Tester does not require knowledge of the programming language, system design or implementation

  • Tester and developer can work independently

  • Helps to identify any ambiguities in the specification

  • Testers evaluate the system based on user requirements; hence there is a higher chance of meeting customer expectations

  • Follows an agile testing method

Black Box Test Steps

The actual steps vary based on the requirements, the size of the project and the strategy. Here are the generic steps to carry out any black box test:

  1. The first step is to study the requirements and specifications of the software, application or system. The software requirement specification (SSR) document is a crucial tool, and black box testers refer to this document often throughout the testing process.

  2. Next, the tester identifies the various inputs and test scenarios, emphasising testing efficiency and time consumption.

  3. The tester then generates test cases focusing on covering the maximum input range.

  4. Testers then run the test cases to generate output. They then compare this output with the expected system output to understand the test results.

  5. If the test is unsuccessful, which means if the generated output differs from the expected values, the testing team sends the feedback to the software development team.

  6. The software development team works on fixing the defects.

  7. The testing team reruns the specific tests to confirm the outputs and ensures there are no errors.


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