Testing & Security

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.

Integrate payment gateways like Stripe, PayPal, and Square with backends for payment processing, subscription management, and webhook handling. Use when building e-commerce platforms, implementing billing systems, and handling payments securely.

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

Configure HTTP security headers including CSP, HSTS, X-Frame-Options, and XSS protection. Use when hardening web applications against common attacks.

Implement event sourcing and CQRS patterns using event stores, aggregates, and projections. Use when building audit trails, temporal queries, or systems requiring full history.

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.

Comprehensive financial analysis workflow covering ratio analysis, trend analysis,benchmarking, and variance analysis. Delivers documented, audit-ready insights.

Create serverless functions on Azure with triggers, bindings, authentication, and monitoring. Use for event-driven computing without managing infrastructure.

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

Gate 4 of development cycle - dispatches 3 specialized reviewers (code, business-logic,security) in parallel for comprehensive code review feedback.

Prevent Cross-Site Scripting (XSS) attacks through input sanitization, output encoding, and Content Security Policy. Use when handling user-generated content in web applications.

Measure relationships between variables using correlation coefficients, correlation matrices, and association tests for correlation measurement, relationship analysis, and multicollinearity detection

Implement secure OAuth 2.0, OpenID Connect (OIDC), JWT authentication, and SSO integration. Use when building secure authentication systems for web and mobile applications.

Comprehensive mobile app testing strategies for iOS and Android. Covers unit tests, UI tests, integration tests, performance testing, and test automation with Detox, Appium, and XCTest.

Month-end and year-end close workflow covering journal entries, reconciliations,close procedures, and audit preparation. Delivers accurate, timely close with full audit trail.

Design property-based tests that verify code properties hold for all inputs using automatic test case generation. Use for property-based, QuickCheck, hypothesis testing, generative testing, and invariant verification.

Implement static code analysis with linters, formatters, and security scanners to catch bugs early. Use when enforcing code standards, detecting security vulnerabilities, or automating code review.

Design and analyze A/B tests, calculate statistical significance, and determine sample sizes for conversion optimization and experiment validation

Develop Ruby on Rails applications with models, controllers, views, Active Record ORM, authentication, and RESTful routes. Use when building Rails applications, managing database relationships, and implementing MVC architecture.

Agent testing methodology - run agents with test inputs, observe outputs,iterate until outputs are accurate and well-structured.