MCP & Protocol Testing / Scenario
The Flaky FastMCP Test Harness
A pytest suite spawns the server as a subprocess, sleeps 3 seconds, and greps JSON strings. Port conflicts and timeouts every third CI run. There is a one-line better way.
- Difficulty
- Hard
- Format
- Scenario
- Points
- 200
- Estimate
- 14 min
// MISSION BRIEF
Your Mission
The team tests their FastMCP server the way they would test any web service: boot it as a subprocess on a port, sleep, then poke it over HTTP. CI disagrees with this plan several times a week.
Read the harness and the CI failures, then redesign the suite around FastMCP's in-memory testing story. Decisions are weighted.
// FIRST CONTACT
Battle teaser
First artifact
conftest.py (current harness)
The structural fix for this harness:
- AMove the tests to a nightly job where flakes are less visible
- BRandomize the port per run and raise the sleep to 10 seconds
- CAdd retries around every HTTP call until it stops failing
- DImport the server object and pass it straight to fastmcp.Client: async with Client(mcp) as client, an in-memory transport with no subprocess, no port, no sleep, and deterministic startup
Answers, scoring, hints, and the full battle stay sealed.
// SKILL TAGS
fastmcpin-memory-testingpytestci-cd