A good progression would be:
L1 → Understand MCP architecture + JSON-RPC + tools
L2 → Explore MCP Inspector + schemas + tool calls
L3 → Test positive, negative, boundary, error and security scenarios
L4 → Automate CLI/API-based MCP tests
L5 → Engineer performance, authorization, reliability and CI/CD testing
The official MCP specification is worth using as the source of truth for tool behavior and contracts.