Static testing and dynamic testing are two of the most crucial tools available to a software developer. Each plays a vital role in securing the software development lifecycle – but in order to get the most out of each type of testing, and choose the right tools for a given situation, it’s crucial to understand the benefits and limitations of each.
The Objectives of Static Testing and Dynamic Testing
Whilst both static and dynamic testing set-out to uncover vulnerabilities and coding errors within a piece of software, they each use different methods for doing so.
Static security testing is used to analyse software in a non-runtime environment – when the software is inactive, and not in operation. This allows developers to perform a thorough inspection of every aspect of the software’s source code, in order to identify and remedy any flaws, back-doors, and in some instances, malicious code. Static testing is often referred to as verification: the evaluation of the development process.
Dynamic testing is performed in a runtime environment, with security analysis carried out whilst software is in operation. With a given input, the software’s actual output is compared to its expected output. This allows developers to analyse the functional behaviour of a piece of software, and monitor its interaction with system memory, CPU function and overall system performance. Dynamic testing is often referred to as validation: the evaluation of a finished product.
Each approach analyses a different aspect of software security, and both validation and verification play an essential role. In order to ensure a secure software development lifecycle, both static and dynamic testing should be deployed. To determine which type of test is most relevant in a given situation, it’s important to understand the benefits and limitations of each.
The Benefits of Static Testing
- Static testing is more comprehensive than dynamic testing. Whilst dynamic testing only reveals errors in executed code, static testing allows developers to analyse source code with a fine-tooth comb.
- Static tests are primarily used as a preventative measure during the early stages of the software development cycle. They allow developers to pick-up on vulnerabilities and errors before development is complete and the software is rolled-out.
- Bugs found during the development process are relatively cheap and easy to fix, making static testing very cost-effective. It also offers a significant return on investment – preventing the spiralling costs associated with errors that end-up built into a finished product.
- With low costs, static testing can be used repeatedly throughout the development process.
The Benefits of Dynamic Testing
- Dynamic testing can reveal vulnerabilities and flaws that may be too subtle or complicated for static analysis to pick-up on.
- Dynamic testing employs a method relatively similar to techniques used by malicious third parties to compromise software, and may offer a quick and efficient way to reveal the most immediate security vulnerabilities.
- Static testing is relatively powerless once software has been released. If a security threat emerges post-rollout, dynamic testing is an essential tool for detecting and remedying the problem.
- Whilst the costs of dynamic testing can be relatively high, the costs of leaving a bug or vulnerability unfixed can be exponentially higher. Dynamic testing allows developers to fix emerging problems quickly and effectively, before security threats can damage the software’s reputation.
Static and dynamic security tests each have their own distinct advantages, and their own unique limitations. Whilst individual circumstances may benefit from one type of test over another, securing the software development lifecycle as a whole requires the structured deployment of both types of testing.
The combined use of static and dynamic testing creates a synergistic relationship between the two approaches: offering combined security benefits much greater than the sum of their individual parts.
