Application programming interfaces have now turned into operational dependencies rather than just being used for peripheral integration in digital government. In Saudi Arabia, the expansion of platform connectivity as part of Vision 2030 is leading to greater consequences from contract defects, authorization errors, inconsistent data exchange, latent service dependencies, and performance regressions. This review presents an advanced framework for API testing and integration validation aimed at ensuring the reliability of digital government systems by drawing on recent evidence from 2020 to 2025 in the areas of REST API testing, microservice assurance, reliability engineering, cybersecurity, and research into Saudi digital government. It finds a consistent gap between endpoint-level functional testing and the more comprehensive assurance needed for public services that involve identity, data, payment, notification, legacy systems, and inter-agency components. The framework proposed therefore includes five interconnected controls: contract baselining, intelligent risk-weighted test generation, integration-chain validation, resilience and security verification, and an evidence-based reliability gate backed by operational feedback. The synthesis contends that test adequacy should be evaluated on the basis of evidence from the service chain rather than simply counting response codes, and that API quality must take into account traceability, awareness of dependencies, recoverability, privacy, and the impact on citizens. Two implementation tables and two conceptual figures are provided to convert the literature into a model suitable for deployment by Saudi government organisations. The framework offers a coherent architecture based on a review of the literature that links technical testing evidence with governance decisions, thus enabling the continuous validation of rapidly changing digital services while maintaining interoperability, service continuity, and public trust.