mcp-test-runner

MCP server for deterministic local test execution and normalized test result reporting.

mcp-test-runner is the verification layer for codebase onboarding agents. It exposes focused MCP tools for running pytest and Jest, parsing test output, and summarizing coverage so downstream agents can mark claims as verified, unverified, or contradicted by real execution.

Codebase Onboarding Stack

mcp-test-runner is the verification layer in a three-server MCP tool stack for Project 6 wayfinder, a codebase onboarding agent.

• mcp-repo-mapper maps repository structure, languages, entry points, framework evidence, and Python dependency edges.
• mcp-ast-explorer provides symbol-grounded Python definition, signature, reference, call-chain, and class-hierarchy lookups.
• mcp-test-runner runs local pytest/Jest checks and coverage summaries so agent claims can be verified against execution.

In wayfinder, this server turns high-risk code understanding claims into verified, unverified, or contradicted evidence from real test execution.

Status

This repository is a Python-first v1 MCP test runner. It supports bounded pytest execution, Jest command execution, single-test targeting, pytest coverage summaries, and normalized pytest/Jest JSON parsing.

The server does not use an LLM. Test results come from subprocess execution and structured parser output.

Tools

Tool	Purpose
health()	Returns ok for smoke checks.
run_pytest(path, test_filter?, timeout_seconds?, cpu_seconds?, memory_mb?)	Run pytest in a bounded working directory and return raw command output.
run_jest(path, test_filter?, timeout_seconds?, cpu_seconds?, memory_mb?)	Run Jest through npx jest and return raw command output.
run_single_test(path, test_id, framework?, timeout_seconds?, cpu_seconds?, memory_mb?)	Run one pytest node id or one Jest test-name pattern.
parse_test_output(stdout, framework)	Normalize test runner JSON output.
get_coverage_summary(path, framework?, timeout_seconds?, cpu_seconds?, memory_mb?)	Return pytest-cov JSON coverage totals.

Supported Scope

• Python 3.11+ package.
• FastMCP 2.x server.
• pytest execution with JSON report output via pytest-json-report.
• Jest command execution via npx jest --json --outputFile.
• pytest and Jest JSON normalization into one TestRunResult schema.
• Single pytest node id execution and Jest test-name targeting.
• pytest-cov coverage summary from .coverage.json.
• Subprocess timeout plus POSIX resource.setrlimit CPU / memory caps.

Current Limitations

• v1 does not use Docker. It uses cwd validation, subprocess timeouts, and POSIX resource limits.
• Resource limits require a POSIX platform that supports resource.setrlimit.
• Jest execution expects Node.js plus project-local or npx-resolvable Jest.
• Jest single-test targeting uses --testNamePattern; it does not parse Jest file-specific node ids.
• Coverage summary is pytest-only in v1.
• Tools return raw command output for execution; call parse_test_output to normalize framework JSON.

Local Development

Install dependencies:

uv sync --extra dev

The PyPI distribution name is lovranran-mcp-test-runner because mcp-test-runner is already taken on PyPI. The installed console script remains mcp-test-runner.

Run the MCP server:

uv run mcp-test-runner

Run verification:

uv run ruff check .
uv run mypy
uv run pytest

License

MIT