Unit Testing

Design and execute performance tests to measure response times, throughput, and resource utilization. Use for performance test, load test, JMeter, k6, benchmark, latency testing, and scalability analysis.

Execute comprehensive disaster recovery tests, validate recovery procedures, and document lessons learned from DR exercises.

Detect unintended visual changes in UI by comparing screenshots across versions. Use for visual regression, screenshot diff, Percy, Chromatic, UI testing, and visual validation.

RED-GREEN-REFACTOR implementation methodology - write failing test first, minimal implementation to pass, then refactor. Ensures tests verify behavior.

Integrate automated testing into CI/CD pipelines for continuous quality feedback. Use for continuous testing, CI testing, automated testing pipelines, test orchestration, and DevOps quality practices.

Implement backup and restore strategies for disaster recovery. Use when creating backup plans, testing restore procedures, or setting up automated backups.

This skill should be used when editing Python code in the erk codebase. Use when writing, reviewing, or refactoring Python to ensure adherence to LBYL exception handling patterns, Python 3.13+ type syntax (list[str], str | None), pathlib operations, ABC-based interfaces, absolute imports, and explicit error boundaries at CLI level. Also provides production-tested code smell patterns from Dagster Labs for API design, parameter complexity, and code organization. Essential for maintaining erk's dignified Python standards.

Structured workflow for disaster recovery planning, implementation, and testing including RTO/RPO definition, DR strategy selection, and failover procedures.

Gate 2 sub-skill - validates uncertain mappings from Gate 1 and confirms all field specifications through testing.

Handle cross-platform compatibility including file paths, environment detection, platform-specific dependencies, and testing across Windows, macOS, and Linux. Use when dealing with platform-specific code or OS compatibility.

Create and manage mocks, stubs, spies, and test doubles for isolating unit tests from external dependencies. Use for mock, stub, spy, test double, Mockito, Jest mocks, and dependency isolation.

Conduct statistical tests including t-tests, chi-square, ANOVA, and p-value analysis for statistical significance, hypothesis validation, and A/B testing

Implement feature flags (toggles) for controlled feature rollouts, A/B testing, canary deployments, and kill switches. Use when deploying new features gradually, testing in production, or managing feature lifecycles.

Gate 3 of development cycle - ensures unit test coverage meets threshold (85%+) for all acceptance criteria using TDD methodology.

Test quality guard - prevents testing mock behavior, production pollution with test-only methods, and mocking without understanding dependencies.

Write comprehensive unit tests with high coverage using testing frameworks like Jest, pytest, JUnit, or RSpec. Use when writing tests for functions, classes, components, or establishing testing standards.

Implement synthetic monitoring and automated testing to simulate user behavior and detect issues before users. Use when creating end-to-end test scenarios, monitoring API flows, or validating user workflows.

TDD for process documentation - write test cases (pressure scenarios), watch baseline fail, write skill, iterate until bulletproof against rationalization.

Migrate Express.js REST APIs to Fastify with automated testing, performance benchmarking, and schema generation. Use when migrating Express applications to Fastify, modernizing Node.js APIs, improving API performance, or when users mention Express to Fastify migration, Fastify conversion, API modernization, or performance optimization of Express apps.

Design and implement CI/CD pipelines with GitHub Actions, GitLab CI, Jenkins, or CircleCI. Use for automated testing, building, and deployment workflows.