Software testing assesses the quality of the software under development. It requires evaluating an application on several parameters, like comparing the developed functionality against a requirement, stability, performance, and overall user experience.
To meet the various objectives, different types of testing take place within the software testing life cycle. So what is negative testing? It’s sometimes referred to as failure testing or error-path testing, but this kind of testing confirms the application’s stability by testing against purposely introduced incorrect data sets and intentional system failures. Negative testing includes testing how the software responds providing unexpected parameters.
Unlike all other testing types, where encountering error is considered as bugs, noticing error is an expected part of negative testing. It involves validating whether the error messages generated are user-friendly, and if any system exceptions are displayed.
Results from negative testing help isolate system crashes and support developers fixing the issues to make a more reliable application.
Negative testing is all about testing probabilities, the ‘what if’s. For example, what if the user enters an input and the connection fails? The most common example of this kind of testing includes testing for password fields with different data sets, testing a credit card field with incorrect entries, testing other data and field types, and different date formats.
Why we need Negative Testing
A system’s stability cannot be determined by comparing the system against a set of defined requirements. Negative testing takes the testing further than the stated specifications. This is to ensure the system is capable of handling invalid input, misconfigurations, and security lapses. The sole purpose of negative testing is to verify that the applications work flawlessly, even in odd circumstances or with incorrect data sets. Negative testing helps to validate all the error conditions, proper messaging, and eliminate system crashes. Overall, it helps in making the system more stable.
How to determine the Scope and Strategy for Negative Testing
As a type of testing, negative testing is unique. Primarily, the objective of all types of software tests is to verify and validate the system against specified requirements that set out what the system should do. Any variations are logged as bugs and the reports returned to the developers for fixing. On the contrary, this kind of testing focuses on testing the scenarios of what the system should not do, which is rarely available in requirement documents.
The first step in the STLC process is to analyze the requirements, then create test cases based on them. Writing a test case is more straightforward when the objectives and expectations have already been laid out in the requirements. The real challenge starts when trying to determine the scope for something not yet defined. So, how can we plan negative test scenarios, and how much negative testing is sufficient?
The creation or planning of negative tests depends largely on the positive test cases that have been planned. These are test cases prepared for all the happy paths and are based on the requirements. Once the expected path is defined, the next step is to determine all the error path or probable input conditions. Negative test cases are created based on these paths or inputs. Although discovering the negative use cases may be cumbersome, the expected results for all testing stays the same. The objective of negative testing is to ensure that the user receives a valid response or error message, without there being any crashes.
Recalling one of the principles of software testing, we understand that “Exhaustive testing is not possible.” This is true when it comes to negative testing as well. Testing cannot run through every possible flow. An important criterion is conducting a risk assessment and identifying an optimal amount of test to ensure maximum coverage. For negative tests to be most effective, thinking from a user’s perspective is recommended, so you can imagine the kind of errors they might encounter. The success of this kind of testing can depend on the tester’s imagination and knowledge of how to use the application. Before starting to test, it is important to run through the scenarios with the team to eliminate the least likely situations.
Software testing techniques like BVA (boundary value analysis) and ECP (equivalence class partition) are the two most widely used techniques for determining negative test scenarios.
During the unit tests review, developers ensure the code works as per the requirements, but reviewing all possible paths is not feasible. When the software reaches QA, the testers will return to testing the same thing again and ensure that every requirement is implemented as expected. Developers rely a lot on QA feedback, especially for negative testing, since this is done mostly during the QA cycle. Therefore, negative testing’s value should not be overlooked because it helps ensure that the system can handle unexpected conditions. It offers a smooth experience and helps in discovering any fatal defects caused by missing requirements.