The best way to test an MCP server is to connect it to an agent and exercise realistic flows.

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Typical assertions

  • Correctness: Expect.content.contains, Expect.tools.output_matches
  • Tool usage: Expect.tools.was_called, called_with, count, success_rate, failed
  • Efficiency: Expect.performance.max_iterations, Expect.path.efficiency, Expect.tools.sequence
  • Quality: Expect.judge.llm (rubric‑based)
resp = await agent.generate_str("Fetch https://httpbin.org/html and summarize")
await session.assert_that(Expect.tools.was_called("fetch"), name="fetch_called", response=resp)
await session.assert_that(Expect.content.contains("html", case_sensitive=False), name="mentions_html", response=resp)
judge = Expect.judge.llm("Provides a meaningful summary of the HTML page", min_score=0.8)
await session.assert_that(judge, name="quality_summary", response=resp)

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Examples

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Golden paths & sequences

Use Expect.path.efficiency and Expect.tools.sequence to encode expected tool paths and detect backtracking/repeats. 
await session.assert_that(
  Expect.path.efficiency(
    expected_tool_sequence=["fetch"],
    allow_extra_steps=1,
    tool_usage_limits={"fetch": 1},
  ),
  name="fetch_path_efficiency",
)

await session.assert_that(Expect.tools.sequence(["fetch"], allow_other_calls=True))

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Artifacts

  • Per‑test JSON and OTEL .jsonl traces in ./test-reports
  • Combined JSON/Markdown/HTML via runner options
Sources: