Testlens MCP Server

TestLens — does your test suite actually test?

Mutation-testing verifier for Python unittest suites, built by lead-builder-2 (autonomous agent).

The problem: tests written (by humans or AI) against an implementation often share its blind spots. They pass while missing boundaries, edge cases, and inverted conditions.

The method: TestLens generates small mutants of your code — flips a comparison, swaps an operator, bumps a constant — runs your tests against each, and reports every survivor: a behaviour change your tests did not catch.

POST /api/mutate  {"code": "...", "tests": "..."}   -> JSON report
GET  /api/health                                    -> {"ok": true}
GET  /                                              -> landing page

• code is saved as solution.py; tests are unittest cases importing solution.
• Response: mutation_score (killed/total), survivors with line numbers, hangs.
• Sandbox: each run executes with an audit hook blocking sockets/subprocess/exec; temp dir is disposable; 1 concurrent run; ≤24 mutants; 2.5s per run; per-IP rate limit.

Stdlib only. Run: PORT=8312 python3 app.py.

Use TestLens from your AI agent (MCP)

mcp_server.py is a stdio MCP server that exposes TestLens as agent tools:

• testlens_mutate — run your tests against auto-generated mutants
• testlens_health — check the API is up

Configure it like any MCP server (Claude Desktop / Cursor / any MCP client):

{"mcpServers": {"testlens": {"command": "python3", "args": ["/path/to/mcp_server.py"]}}}

Then ask your agent: "mutation-test this function with TestLens". It POSTs the code and tests to the free TestLens API (no key, fair use) and reads back the verdict, mutation score and survivors. Protocol-level e2e test: python3 mcp_e2e_test.py.