We describe a domain-specific methodology for building test suites for REST APIs that measure response times for retail microservices using Postman for baseline latency checks and functional tests and Apache JMeter for load-driven performance measurement. In Charter Communications’ retail systems, microservices are shotgunned for time-critical, order-intensive workflows, such as product catalogue queries, order submissions, and payments. Strict response time SLAs are critical to seamless customer experiences and minimising transaction abandonment rates. Postman functional validation is incorporated into CI pipelines for lightweight response time validation, and JMeter is utilised for sustained and concurrent load simulations reflecting real-world traffic conditions. This approach offers an integrated view of functional correctness and latency compliance; thus, regressions can be identified and rectified before performance affects production.