Chapter 03

Principles of Software Testing

Principles of Software Testing

• "Testing shows the presence of defects" means that testing can only reveal defects that are present in the software, not prove that there are no defects.

• "Exhaustive testing is impossible" means that it is not possible to test every possible combination of inputs and scenarios, so testing has to be done strategically.

• "Early Testing" means that testing should start as early as possible in the development process to find and fix defects early on.

• "Defect Clustering" means that most defects are concentrated in a small number of modules or components.

• "Pesticide Paradox" means that as you test more, you will eventually find fewer defects, but this doesn't mean that the software is defect-free, it might be due to the test cases used are no longer effective.

• "Testing is context dependent" means that the testing approach and test cases will vary depending on the specific context, such as the type of software, its intended use, and the risks involved.

• "Absence-of-errors fallacy" means that the lack of defects found during testing does not necessarily mean that the software is free of defects, it might be due to the limitations of the testing process.

Testing vs. Debugging

Testing and debugging are two different activities that are used to ensure that software is functioning correctly.

Testing is the process of evaluating a system or its component(s) with the intent to find whether it satisfies the specified requirements or not. It is done before the software is released to the customer. The goal of testing is to find defects in the software early in the development process, so that they can be fixed before the software is released.

Debugging, on the other hand, is the process of finding and fixing errors or bugs in the software. It is done after the software has been developed and is typically done in response to a problem or error that has been found during testing or in the field. The goal of debugging is to locate and correct the problem so that the software can function correctly.

In short, testing is the process of finding defects, while debugging is the process of fixing those defects.

What is a Test Scenario?

A test scenario is a description of a specific situation or set of conditions that a software program or system is expected to handle during testing. It provides a specific example of how the software should behave in a particular situation, and is used to test that the software is functioning correctly in that situation.

A test scenario is usually written in natural language and describes the steps that will be taken to perform the test, the expected outcome, and any conditions that must be met for the test to be valid. It is a high-level description of what will be tested and it is the basis for creating detailed test cases which will be executed to check the software against the scenario.

For example, a test scenario for an online shopping website could be: "As a customer, I want to be able to search for products on the website, so that I can find what I am looking for easily." This scenario would be used to test that the search feature of the website is working correctly and returns the expected results.

How to Write Test Scenarios?

Writing test scenarios is a process of identifying different ways in which the software might be used and then creating specific examples of those situations to test the software. Here are the general steps to follow when writing test scenarios:

• Understand the requirements: Understand the requirements of the software and what it is supposed to do. This will help you identify the different ways in which it might be used.

• Identify the scenarios: Identify the different scenarios in which the software might be used. These scenarios should be based on the requirements and should cover all the major functionality of the software.

• Write the scenarios: Write the scenarios in natural language, describing the steps that will be taken to perform the test, the expected outcome, and any conditions that must be met for the test to be valid.

• Review and refine: Review the scenarios to make sure they are complete and accurate. Refine the scenarios if necessary.

• Create test cases: Use the scenarios as the basis for creating detailed test cases that will be executed to check the software against the scenario.

• Prioritize: Prioritize the scenarios based on the importance and risk.

It's important to keep in mind that test scenarios should be simple, easy to understand, and should not contain too much technical details.

Standard Test Case Format

• Test Case ID: A unique identifier for the test case, usually in the form of a number or short code.

• Test Scenario: A brief description of the scenario that the test case is testing.

• Test Steps: Detailed instructions on how to perform the test, including the actions to be taken and the inputs to be provided.

• Prerequisites: Any conditions that must be met before the test can be run, such as specific software or hardware configurations.

• Test Data: The data that will be used during the test, such as input values and expected output values.

• Expected/Intended Results: The expected outcome of the test, such as the expected behavior of the software or the expected values of specific variables.

• Actual Results: The actual outcome of the test, as observed during the test execution.

• Test Status: The outcome of the test, either "Pass" if the test was successful or "Fail" if the test did not produce the expected results.

It's important to note that test cases should be written in a clear, concise and easy to understand language, so that they can be understood by the person executing the test, even if they are not familiar with the software. Additionally, test cases should be maintainable, so that they can be updated as the software evolves.

Test Scenarios vs. Test Cases.

Test Scenarios and Test Cases are both used in software testing, but they serve different purposes and have different levels of detail.

Test Scenarios are high-level descriptions of what will be tested and provide an overview of the different situations or conditions that the software might be used in. They are usually written in natural language and provide a general idea of what the test is trying to accomplish. Test scenarios are often used to create a testing plan and to identify the overall testing objectives.

Test Cases, on the other hand, are more detailed instructions on how to perform a specific test. They provide step-by-step instructions on what actions to take and what inputs to provide, as well as the expected outcome of the test. Test cases are usually written in a structured format and are used to execute the test and check the software against the scenario.

In simple terms, Test Scenarios are the blueprint that outlines the objectives of the testing and Test Cases are the detailed instructions that are used to execute the test.