3. GuidanceVerifying implementation refers to the activity of verifying that the software requirements, including interface requirements, have been implemented. Specific to a software project's implementation, verification involves confirming that the implementation (code) correctly, completely, consistently, and accurately includes each software requirement. Verification methods can include testing, analysis, demonstration, and inspection. Per NPR 7150.2, “testing verifies the code against the requirements and the design to ensure that the requirements are implemented. Testing also identifies problems and defects that are corrected and tracked to closure before product delivery. Testing also validates that the software operates appropriately in the intended environment.” “Software item qualification testing is performed to demonstrate ... that software item requirements have been met. It covers software items requirements in the Software Requirements Specifications (SRSs) and in associated Interface Requirements Specifications (IRSs),”  including interface control documents (ICDs) and hardware interface requirements. The software testing should be performed using the target hardware. The target hardware used for the software testing should be as close as possible to the operational target hardware and should be in a configuration as close as possible to the operational configuration. The software test cases should cover “verification of all software requirements under conditions that are as close as possible to those that the software will encounter in the operational environment (e.g., operational data constraints, operational input and output data rates, operational scenarios, target hardware configurations); verification of all software interface requirements, using the actual interface wherever possible or high-fidelity simulations of the interface where not possible; verification of all software specialty engineering requirements (e.g., supportability, testability, dependability/reliability/maintainability/availability, safety, security, and human systems integration, as applicable), including in particular verification of software reliability requirements and fault detection, isolation, and recovery requirements; stress testing, including worst–case scenarios; and resource utilization measurements (e.g., CPU, memory, storage, bandwidth). All software requirements should be verified by software ... testing whether they are satisfied by COTS, reuse... or newly developed software.” The NASA Independent Verification and Validation Technical Framework (IVV 09-1) document  states that "It is important to recognize that requirements cannot be evaluated in isolation. Requirements must be evaluated as a set in order to determine that a particular goal or behavior is being met." Confirmation of software requirements implementation needs to occur at various times in the project life cycle to ensure that any issues are found and corrected as early as possible: - Peer reviews.
- Traceability analyses.
- Completion of units of code.
- Integration testing.
- System testing.
The NASA Independent Verification and Validation Technical Framework (IVV 09-1) document states that "It is important to recognize that requirements cannot be evaluated in isolation. Requirements must be evaluated as a set in order to determine that a particular goal or behavior is being met." |
Verification of requirements implementation includes the following objectives: - Ensure that the source code reliably performs capabilities stated in the requirements under nominal and off-nominal conditions, as applicable to the software classification (NASA IV&V Technical Framework , Revision M).
- Ensure that the source code provides the reliability and fault tolerance stated in the requirements, as applicable to the software classification (NASA IV&V Technical Framework , Revision M).
- Ensure that the source code satisfies functional, performance, and other requirements (Software Development Process Description Document
 , Revision R).
While the primary means of implementation verification is testing, the following analysis techniques are also useful (Software Development Process Description Document , Revision R). Note that these techniques are useful for detecting coding issues and may not necessarily be required for verifying that the software properly implements the requirements unless the requirements include statements related to the complexity, memory usage, coding standards, etc. - McCabe complexity analysis (measures the number of linearly independent paths through a program's source code).
- Memory analysis.
- Static analysis.
- Code standards checking.
Requirements implementation verification activities need to be planned and documented (Software Test Plan) and verification techniques can be included in the bidirectional requirements traceability matrix (SWE-072) to ensure that all requirements are verified in the implementation. Results of this activity are to be documented (SWE-069), evaluated (SWE-068), and defects corrected. NASA users should consult Center Process Asset Libraries (PALs) for Center-specific guidance and resources related to implementation verification. |
Additional guidance related to software testing, including specifics of plan, procedure, and report contents may be found in the following related requirements in this handbook: |