pytest-mcp-plugin 0.2.3

pytest for MCP servers — the testing framework for the Model Context Protocol

pytest-mcp-plugin

pytest for MCP servers — the testing framework for the Model Context Protocol.

pip install pytest-mcp-plugin
mcp-test demo            # runs a bundled MCP server + tests in 5 seconds

Note on the name. This package is published on PyPI as pytest-mcp-plugin. The mcp-test name on PyPI is reserved by Anthropic for their official MCP SDK, and PyPI's name-similarity policy blocks close variants like mcptest. The CLI binary is still mcp-test, and the Python module is still mcp_test.

---

Why

MCP (Model Context Protocol) is the standard interface every AI agent now uses to talk to tools, files, databases, and APIs. Thousands of teams are shipping MCP servers in 2026. Almost none of them are tested.

pytest-mcp-plugin fixes that. Write tests for your MCP tools, resources, and prompts with the same developer experience you expect from pytest.

• pytest plugin with auto-registered fixtures
• stdio and HTTP/SSE transports
• Schema validation, snapshot testing, coverage reports
• Auth + policy assertions
• Drop-in GitHub Action

---

60-second tour

pip install pytest-mcp-plugin
mcp-test demo

That spins up a bundled MCP server and runs a real test suite against it — no setup, no API keys, no servers to write first.

🚀 mcp-test demo
   server  : python -m mcp_test._demo_server
   workdir : /tmp/mcptest-demo-xxxx

test_demo.py::test_lists_tools         PASSED
test_demo.py::test_echo                PASSED
test_demo.py::test_add                 PASSED
test_demo.py::test_uppercase           PASSED
test_demo.py::test_fail_returns_error  PASSED

✅ Demo passed. Now write tests for your own MCP server:
   mcp-test init

---

Test your own server

cd my-mcp-server/
mcp-test init
pytest --mcp-command "python my_server.py" -v

Or pin the command in your pyproject.toml:

[tool.mcp-test]
command = "python my_server.py"
timeout = 10

[tool.mcp-test.timeouts]
"tools/list" = 5
"tools/call" = 30
"sampling/createMessage" = 60

…and just run:

mcp-test run

---

Write tests

# tests/test_my_server.py
from mcp_test import assert_tool_ok, assert_tool_error, assert_tool_text_contains


def test_search_returns_results(mcp_client):
    result = mcp_client.call_tool("search", query="machine learning")
    assert_tool_ok(result)
    assert len(result.content) > 0


def test_search_handles_empty_query(mcp_client):
    result = mcp_client.call_tool("search", query="")
    assert_tool_error(result)


def test_search_schema(mcp_client):
    tools = mcp_client.list_tools()
    search = tools.find("search")
    assert search.required == ["query"]
    assert search.properties["query"]["type"] == "string"

Use as a library

from mcp_test import MCPTestClient

with MCPTestClient.from_command("python my_server.py") as client:
    tools = client.list_tools()
    print(tools.names())

    result = client.call_tool("echo", message="hello")
    print(result.text())

---

Run on every PR (GitHub Action)

pytest-mcp-plugin ships as a composite action you can drop into any repo:

# .github/workflows/mcp-tests.yml
name: MCP Tests

on:
  pull_request:
  push:
    branches: [main]

jobs:
  mcp-test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: yagna-1/mcp-test@v0.2.0
        with:
          command: "python my_server.py"
          test-dir: "tests"

That's it. The action installs pytest-mcp-plugin, runs your suite against your MCP server, and posts a JUnit XML report.

---

CLI reference

Command	Description
mcp-test demo	Run the bundled demo server + tests (zero setup)
mcp-test init	Scaffold tests/ with example MCP tests
mcp-test run -c "python server.py"	Run pytest against your server
mcp-test snapshot -c "..."	Run snapshot tests (--update to refresh)
mcp-test coverage -c "..."	Print coverage report (tools/prompts/resources)
mcp-test validate -c "..."	Validate tool input schemas
mcp-test conformance --url "..."	Run the upstream MCP conformance suite through npx
mcp-test bench -c "..."	Run lightweight p50/p95/p99 regression probes

All commands accept --help for full options.

---

Fixtures

The pytest plugin auto-registers three fixtures:

Fixture	Scope	Use for
mcp_client	session	Fast — one server process for the whole test run
mcp_client_fresh	function	Clean state per test
sandboxed_client	function	Fresh server with cwd=tmp_path and DATA_DIR=tmp_path
snapshot	function	Snapshot testing helper

pytest --mcp-command "python my_server.py" --mcp-timeout 15 \
  --mcp-timeout-method tools/call=30 \
  --mcp-trace .mcp-test/trace.jsonl

--mcp-timeout-method METHOD=SECONDS may be passed multiple times, and the same values can live in [tool.mcp-test.timeouts]. --mcp-trace records JSONL wire frames; in CI, failing tests also dump recent frames to mcp-traces/.

Use mcp-test conformance --url ... --pytest-items when you want each parsed upstream scenario re-emitted as a normal pytest test item.

Spec-version markers

Mark tests by required MCP spec version; the plugin auto-skips tests against older servers.

import pytest

@pytest.mark.mcp_v3  # requires spec >= 2025-06-18
def test_uses_recent_feature(mcp_client):
    ...

Available markers: mcp_v2, mcp_v3, mcp_v4.

Assertion helpers

from mcp_test import (
    assert_tool_ok,
    assert_tool_error,
    assert_tool_error_code,
    assert_tool_text_contains,
    assert_tool_text_equals,
    assert_tool_content_count,
    assert_policy_allows,
    assert_policy_blocks,
    assert_task_completes_within,
    assert_task_cancelled,
    assert_task_failed,
)

---

Architecture

pytest-mcp-plugin runs your MCP server as a subprocess and speaks JSON-RPC 2.0 over stdio (or HTTP/SSE for the HTTP transport). A background message pump handles response routing, notification dispatching, and concurrent request support — so your tests just work.

Source modules:

mcp_test/
  client.py            # stdio JSON-RPC client
  http_client.py       # HTTP + SSE client
  plugin.py            # pytest plugin (fixtures, options, markers)
  cli.py               # mcp-test CLI
  assertions.py        # assert_tool_*, assert_policy_*, assert_task_*
  schema_validator.py  # JSON Schema validation for tool inputs
  coverage.py          # tools/prompts/resources coverage tracker
  snapshot.py          # snapshot testing
  auth.py              # OAuth / PKCE / RFC 9728 helpers
  bench.py             # lightweight regression benchmark probes
  conformance.py       # bridge to @modelcontextprotocol/conformance
  compliance.py        # conformance score helpers
  fastmcp.py           # in-process FastMCP harness adapter
  replay.py            # deterministic wire-trace replay lookup
  pagination.py        # cursor pagination helpers
  test_packs.py        # reusable server-shape test packs
  timeouts.py          # per-method timeout policy
  wire_trace.py        # JSONL wire trace recorder
  types.py             # ToolResult, ToolSchema, MCPError, ...
  _demo_server.py      # bundled demo server (used by `mcp-test demo`)

Status

pytest-mcp-plugin is beta. The CLI surface and plugin API are stable; minor internals (schema validator details, snapshot format) may still change.

Roadmap

See ROADMAP.md for what's next, what we explicitly won't build, and how we plan to complement (not compete with) Anthropic's official @modelcontextprotocol/conformance and @modelcontextprotocol/inspector.

Contributing

Bug reports, feature requests, and PRs welcome at github.com/yagna-1/mcp-test.

License

MIT