The role of functional testing in application security

The role of functional testing in application security

Editorial team


January 26, 2022

Application Security Testing (AST) is an essential part of the software development process. It ensures that applications are built to specifications and can be used reliably in production environments. This article explores a type of software testing called functional testing. Functional testing is an important part of application security because it verifies that functionality works as intended without exposing sensitive information or attack vectors to hackers.

This article discusses the role of functional testing in application security and provides guidance for performing this type of testing effectively.

What is functional testing?

Functional testing is a software testing technique that verifies the functionality of software. The purpose of functional testing is to ensure that software features work as expected. This type of testing ensures that the software works properly and meets the requirements specified by the user. Functional testing is primarily a black box and as such does not involve application source code.

Importance of Functional Testing in AppSec

Functional testing is one of the most important aspects of application security. Functional testing verifies that software functionality works as intended, which is critical to ensuring the security of an application. Functional testing is an important part of the software development lifecycle and should be done early in the development cycle to ensure the application is secure.

Benefits of a Successful Functional Test

The benefits of a successful functional test are:

  • The software works as expected and meets the requirements specified by the user.
  • The software is free from functional errors and vulnerabilities.
  • The software is stable and reliable, which ensures optimal functional performance.
  • Compliance with security policies and a high level of rigor in application security testing.

Functional vs. fuzzing testing

Functional testing differs from fuzzing in that functional testing mainly checks that the functional requirements of the software are met while fuzzing checks for functional errors in the software. Fuzzing is a crawler that constantly tries different combinations of inputs to trigger different behaviors, and errors can be generated if those behaviors don’t match the application specifications. Errors don’t have to be just security vulnerabilities, they can also be specification violations.

An advantage of using an advanced fuzzer such as Mayhem is that it extends forms of functional testing by parameterizing the test in a byte array and then looking for input byte strings that trigger bugs. Even better, developers can run a fuzz test case in less time than it typically takes to write individual functional unit tests. Additionally, fuzzing tools like Mayhem can easily be configured for automation testing, easing the burden on developers and supporting continuous integration.

Functional Testing vs Non-Functional Testing

Functional testing differs from non-functional testing in that functional testing focuses on verifying the functional requirements of the software, while non-functional testing is used for performance testing and checks for performance issues, usability issues, and performance issues. other issues that are not directly related to functional use cases. .

Types of functional tests

functional test types like gates

There are several types of functional tests that can be used to test the functionality of a software application. These include:

Unit tests

Unit testing is used to test individual units or components of a software program. This type of testing is important because it helps identify and fix errors in the code before they can be exploited. A unit test is usually performed by the developers who wrote the code and helps ensure the quality of the code.

The main purpose of unit testing is to verify that individual units of code work as expected. This type of test is performed by checking the output of each unit against the expected output. Unit tests should be easy to write and run, and should be reliable and fast.

Component testing

Component testing, also known as module testing, is a type of software testing used to test individual components or modules of a software program. Component testing is usually done by developers and usually takes place after unit testing.

The primary purpose of module testing is to verify that individual units of code work as expected. This type of test is performed by checking the output of each unit against the expected output.

Smoke test

Smoke tests are designed to identify the most common software functional and integration issues with minimal development effort. The name comes from electronics where it is used to detect gross component failures before they are installed in a system for final functional check. In software development, it is the process of ensuring that new code works properly before it goes into production. A smoke test case failure will cause the code to roll back to the initial development stage.

Integration testing

Integration testing, also known as functional interface testing, is a type of software testing that involves functional testing of the integrated parts of an application. This type of testing is usually done after unit testing and system testing.

The goal of integration testing is to catch errors that occur when different parts of an application are combined. These errors can be caused by incorrect data, incompatible functions, or incorrect sequencing of events. An example of functional integration testing would be functional testing performed after integrating a new module into an existing application.

Regression testing

Regression testing reruns functional and non-functional tests to ensure that previously developed and tested software still works after submitting new code commits.

In the area of ​​application security, functional testing is an important method for validating that newly implemented functions do not introduce new vulnerabilities into existing code that had been previously secured. Failure of a regression test would mean that a feature added to the software inadvertently resulted in a new bug or vulnerability.

mental health test

Sanity Testing is a non-exhaustive test that confirms whether an application’s functionality works as expected in certain basic scenarios, without going into the details of validation and exit functionality. It follows the logic that if a basic function fails, the more advanced functions that follow will also fail. Mental health tests fall under the category of regression tests.

Negative test

Negative testing is a black box testing technique that is used to identify errors by simulating invalid or unexpected entries in the system. It can be used to test functional and non-functional requirements. Unlike positive tests, which aim to verify that the system works as expected, negative tests attempt to find ways to break the system.

API testing

API testing is a functional testing approach where the application programming interface (API) is tested by making requests using a computer program to check for functional defects. It is often used in application security and functional testing to verify that a software or web product operates according to its specifications.

User acceptance test

User Acceptance Testing is another functional testing method that should be performed on the application after the previous functional testing is complete and before it is handed over for release.

The purpose of functional testing is to answer the question “are we building the right thing?” while the objective of UAT is to answer the question “are we building this right?”

Running a Successful Bump Test

successful functional test shown as a bullseye

When it comes to functional testing, there are a few key things you need to keep in mind in order to ensure successful execution.

Understand the requirements

First, it is important to fully understand the business requirements and what is expected of the application. This will help you focus your testing efforts on the right areas.

Cover all scenarios

Second, you need to have a good set of test cases covering all possible scenarios. This will help ensure that all aspects of the application are tested.

Secure Resources

Third, you need to ensure that you have adequate resources to perform the tests. This includes both people and tools.

Controlled environment

Fourth, you must ensure that the test case and environment are set up correctly and that functional testing can be performed in a controlled environment.

Test Automation

Finally, you need to ensure that functional tests are repeatable and can be run as automated tests so that they run continuously.


Functional testing is a crucial step in the software development lifecycle. This helps ensure that newly implemented features do not introduce new functional flaws and vulnerabilities into existing code and serves as a quality assurance measure for software development.

When performing functional tests, it is important to understand requirements, cover all scenarios, secure resources, establish a controlled environment, and automate functional tests as much as possible so that they can be performed. run continuously. By doing so, you will be able to run successful functional tests and ensure that newly developed applications do not introduce new functional or application security flaws.

You can learn more about application security testing and fuzzing exploring our Blog and Resources pages.

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