API Test Suite Builder Skill for Claude

API Test Suite Builder

Scan API route definitions across frameworks (Next.js App Router, Express, FastAPI, Django REST, Go net/http), analyze request/response schemas, and generate comprehensive test suites covering authentication, authorization, input validation, error handling, pagination, file uploads, rate limiting, contract testing, and load testing. Outputs ready-to-run test files for Vitest+Supertest (Node), Pytest+httpx (Python), or k6 (load testing).

Core Capabilities

• Route detection & analysis — scan source files to extract endpoints, parse request/response schemas, detect auth middleware and authorization rules across Node, Python, and Go frameworks.
• Test matrix generation — auth (valid/invalid/expired tokens, wrong roles), input validation (missing/wrong-type/boundary/injection), error paths (400/401/403/404/409/422/429/500), pagination, file uploads, and rate limiting.
• Contract testing — OpenAPI-to-test generation, Pact consumer-driven contracts, schema snapshot testing for breaking-change detection.
• Load testing — k6 scripts with ramp-up patterns and SLA thresholds, latency percentile tracking (P50/P95/P99), concurrent user simulation.

When to Use

• New API added — generate a test scaffold before implementation (TDD).
• Legacy API with no tests — scan and generate baseline coverage.
• Pre-release — ensure all routes have at least smoke tests.
• API contract change — detect and test breaking changes.
• Security audit — generate adversarial input tests.
• Performance validation — create load-test baselines.

Clarify First

Before generating the suite, confirm these inputs. If any is unknown or vague, ASK — do not assume:

• [ ] Target framework — Vitest+Supertest, Pytest+httpx, or k6 (determines the emitted test-file format via --framework)
• [ ] Spec or routes source — an OpenAPI spec or the source files to scan (the input the generator parses)
• [ ] Test scope — auth, input validation, contract, load, or the full matrix (which test categories get generated)

Stop rule: ask only the 2-3 that most change the output. If the user says "just draft it," proceed and list your assumptions at the top of the artifact.

Tools

| Tool | Purpose | Command |

|------|---------|---------|

| test_generator.py | Generate API test skeletons from an OpenAPI/Swagger spec | python scripts/test_generator.py spec.json --framework vitest --output tests/ |

| coverage_analyzer.py | Compare spec endpoints vs existing test files to find gaps | python scripts/coverage_analyzer.py spec.json tests/ --threshold 95 |

| contract_validator.py | Validate response samples against OpenAPI schema contracts | python scripts/contract_validator.py spec.json samples/ --strict |

References

Load the reference that matches the task — keep this file lean and pull detail on demand:

• references/route-detection-and-matrices.md — per-framework route-detection shell commands and the full auth / input-validation / pagination test matrices with worked TypeScript examples. Read when scanning a codebase or writing the core test cases.
• references/contract-and-load-testing.md — complete Pact consumer-driven contract test and k6 load-test scripts, plus the commands to run load tests locally, against staging, and in the cloud. Read when adding contract or performance tests.
• references/workflow-and-quality.md — the 9-step generation workflow, reusable test-helper patterns (auth, authed request, factories), common pitfalls, best practices, a troubleshooting table, and the success-criteria bar. Read before generating a suite and before shipping it.

Scope & Limitations

This skill covers:

• Generating test suites from route definitions for REST APIs across Node.js, Python, and Go frameworks
• Authentication, authorization, input validation, pagination, and error-path test generation
• Consumer-driven contract testing with Pact and schema snapshot validation
• Load and performance testing script generation with k6 and Artillery

This skill does NOT cover:

• GraphQL API testing (see engineering/api-design-reviewer for schema review patterns)
• End-to-end browser testing or UI interaction testing (see engineering/playwright-pro)
• Database migration testing or schema validation (see engineering/database-schema-designer)
• Security penetration testing beyond input sanitization checks (see engineering/skill-security-auditor)

Integration Points

| Skill | Integration | Data Flow |

|-------|------------|-----------|

| engineering/api-design-reviewer | Validate API design before generating tests | Design review output defines the endpoint contracts that this skill generates tests for |

| engineering/ci-cd-pipeline-builder | Embed generated tests into CI/CD pipelines | Generated test files and k6 scripts are added as pipeline stages with pass/fail gates |

| engineering/playwright-pro | Complement API tests with E2E browser tests | API test suite validates backend behavior; Playwright tests validate the frontend consuming those APIs |

| engineering/database-schema-designer | Align test fixtures with database schema | Schema definitions inform factory functions and seed data used in generated test helpers |

| engineering/observability-designer | Monitor test-covered endpoints in production | Load test thresholds (P95, P99) feed into alerting rules for the same endpoints in production dashboards |

| engineering/performance-profiler | Investigate endpoints that fail load test thresholds | k6 results identify slow endpoints; the profiler skill traces root causes at the code level |