Regression testing is a type of software testing that confirms that a recent program or code change has not adversely affected existing features1 It involves re-running functional and non-functional tests to ensure that previously developed and tested software still performs as expected after a change2 Regression testing is suitable for large code sets in environments where time to completion is critical, as it can help detect and prevent defects, improve quality, and enable faster delivery of secure software. Regression testing can be automated to reduce manual errors, speed up feedback loops, and increase efficiency and reliability3

The other options are not correct because:

Option A is not correct because parallel testing is a type of software testing that involves testing multiple applications or subsystems concurrently to reduce the test time4 Parallel testing does not necessarily ensure the integration of security testing, as it depends on the quality and coverage of the test cases and scenarios used for each application or subsystem. Parallel testing may also introduce challenges such as synchronization, coordination, and communication among the testers and developers5

Option B is not correct because full application stack unit testing is a type of software testing that involves testing individual units or components of an application in isolation to verify their functionality, logic, interfaces, and performance6 Full application stack unit testing does not ensure the integration of security testing, as it does not consider the interactions and dependencies among the units or components, or the behavior of the application as a whole. Unit testing is typically performed by developers at an early stage of the software development life cycle, and may not cover all the security aspects or requirements of the application7

Option C is not correct because functional verification is a type of software testing that involves verifying that the software meets the specified requirements and satisfies the user needs. Functional verification does not ensure the integration of security testing, as it does not focus on how the software is designed or configured, or how it handles malicious or unexpected inputs. Functional verification is typically performed by quality assurance teams at a later stage of the software development life cycle, and may not detect all the security vulnerabilities or risks of the software.

References: 1: Wikipedia. Regression testing - Wikipedia. [Online]. Available: 3. [Accessed: 14-Apr-2023]. 2: Katalon. What is Regression Testing? Definition, Tools, Examples - Katalon. [Online]. Available: 4. [Accessed: 14-Apr-2023]. 3: BMC Software. Shift Left Testing: What, Why & How To Shift Left – BMC Software | Blogs. [Online]. Available: 3. [Accessed: 14-Apr-2023]. 4: Guru99. What is Parallel Testing? with Example - Guru99. [Online]. Available: . [Accessed: 14-Apr-2023]. 5: LambdaTest. Parallel Testing In Selenium WebDriver | LambdaTest Blog. [Online]. Available: . [Accessed: 14-Apr-2023]. 6: Guru99. What is Unit Testing? Types & Examples - Guru99. [Online]. Available: . [Accessed: 14-Apr-2023]. 7: Software Testing Help. Unit Testing Vs Integration Testing: Difference Between These Two - SoftwareTestingHelp.com Blog. [Online]. Available: . [Accessed: 14-Apr-2023]. : Guru99. What is Functional Testing? Types & Examples - Guru99. [Online]. Available: . [Accessed: 14-Apr-2023]. : Software Testing Help. Functional Testing Vs Non-Functional Testing - SoftwareTestingHelp.com Blog. [Online]. Available: . [Accessed: 14-Apr-2023].