Testing for container security throughout the software development life cycle (SDLC) is crucial to identify and fix vulnerabilities, but there's no single best approach as it depends on the organization's specifics. Testing locally offers fast feedback cycles but requires individual developer action and may not be comprehensive. Continuous integration and continuous delivery pipelines provide a good gate for testing but may have implementation costs and limitations. Registry-level testing can cover all first-party images with ease, while production-level testing provides an accurate picture of running applications but has slow feedback cycles. Ideally, thorough testing should be done throughout the SDLC to avoid friction between teams and ensure quick deployment.