How to Test MCP Servers (codely.com)

MCPs (Model Context Protocol) have gone from hype to production in under a year: after Anthropic’s spec and a flurry of early adoption, security issues and a formal registry emerged—forcing the community to treat MCPs as first-class contracts. Because MCP primitives (tools, resources, prompts, templates) are entry points that an LLM client uses just like HTTP routes, the article argues they must be tested with the same rigor: to document behavior, prevent silent breakages, and detect regressions across transport layers and storage. Practically, the recommended approach centers on contract-focused end-to-end tests that instantiate a persistent official MCP client, exercise primitives exactly like real clients (including DB hits when needed), and assert structured responses (content, structuredContent, isError). Test suites should mirror MCP primitives and include registration, empty-case, happy-path, error, and regression tests; resource-template tests should validate generated URIs and param completion. The MCP Inspector is useful for manual exploration but inadequate for automated testing (ephemeral connections, untyped responses, incomplete spec). The official client, optionally wrapped in a test-friendly helper, provides persistent connections, full-spec support, transport swapping (stdio↔http) and convenience assertions—making CI-friendly, transport-agnostic MCP testing practical and reliable.