FastMCP tests

Read nearby tests, the testing guide, and the repository's validation requirements first. Extend the owning test module when it remains readable; use a focused module when the existing one is already too large.

For a bug fix, run the regression against unchanged code and confirm it fails for the reported reason, then run it with the fix. An import error or broken fixture is not a reproduced bug. To run a PR's test against main, copy it into a main worktree: pythonpath in pyproject shadows PYTHONPATH. Include supported adjacent behavior that the same branch could change, especially omitted defaults and explicit overrides.

• Async tests need no marker: asyncio_mode = "auto" is configured globally.
• Use Client(server) for real MCP dispatch without a network server. Use HTTP transport only when network behavior is the subject.
• Test the default protocol mode; pin mode="legacy" only when the handshake era is the subject.
• Mock external boundaries, not the FastMCP functions under test. For OpenAPI requests, capture the outgoing request with httpx2.MockTransport and assert its bytes, headers, or decoded parameters.
• Keep imports at module scope. Prefer function-scoped fixtures and tmp_path for files.
• Parameterize variations of one contract; separate unrelated behavior. For JSON, equality alone does not distinguish True from 1: check the resulting type when type preservation matters.
• Use existing inline_snapshot conventions for complex schema assertions. Inspect generated snapshots rather than accepting them blindly.
• The default timeout is five seconds. Use the repository's integration conventions for tests that legitimately need more time.