Portability testing is concerned with how well software can be transferred from one environment to another. In the context of a bank using COTS (Commercial Off-The-Shelf) software, the sub-characteristic of replaceability becomes particularly relevant. This is because the bank does not want to create a dependency on any external COTS supplier, meaning it should be able to replace the software with another product without significant effort or operational disruption. Replaceability ensures that if needed, the bank can switch to different software, thereby mitigating the risk of supplier dependency.