Claude Code testing

Critical Business Logic Has No Test Coverage

Your test suite covers utility functions and simple CRUD operations but completely misses the critical business logic: payment processing, access control checks, data transformations, and state machine transitions. The parts of your code that are most likely to cause catastrophic failures if broken have zero test coverage.

Claude Code tends to generate tests for the easiest-to-test code (pure functions, simple helpers) while skipping the complex, stateful, integration-heavy code that actually needs testing the most. The coverage report may show 70% overall but the missing 30% contains all the high-risk logic.

This becomes painfully apparent when a 'small refactor' of the payment flow introduces a bug that charges customers the wrong amount, and no test catches it before production.

Error Messages You Might See

Payment charged wrong amount in production User accessed admin panel without admin role Data export missing records for edge case State transition allowed that should be blocked
Payment charged wrong amount in productionUser accessed admin panel without admin roleData export missing records for edge caseState transition allowed that should be blocked

Common Causes

  • Complex setup avoided — Tests for payment flows require Stripe test mode, database seeding, and multi-step setup that AI skips
  • External service dependencies — Code that calls external APIs is left untested because mocking the API is complex
  • State machine transitions untested — Status changes (pending -> processing -> completed -> failed) and their edge cases have no coverage
  • Error handling paths untested — Only the happy path is tested; what happens on timeout, invalid input, or partial failure is unknown
  • Coverage metrics misleading — Line coverage is high because simple code is tested, but branch coverage on critical paths is zero

How to Fix It

  1. Identify critical paths first — List your top 10 most important features (payment, auth, data export). These get tests first regardless of overall coverage
  2. Write integration tests for critical flows — Test the full flow from request to database, using test databases and service test modes (Stripe test keys)
  3. Test every state transition — For each status field, test every valid transition AND verify invalid transitions are rejected
  4. Test error handling explicitly — Force errors (network timeouts, invalid data, permission denied) and verify the app handles them gracefully
  5. Use branch coverage, not line coverage — Configure your coverage tool to report branch coverage. Aim for 100% branch coverage on critical paths

Real developers can help you.

Matt Butler Matt Butler Software Engineer @ AWS Caio Rodrigues Caio Rodrigues I'm a full-stack developer focused on building practical and scalable web applications. My main experience is with **React, TypeScript, and modern frontend architectures**, where I prioritize clean code, component reusability, and maintainable project structures. I have strong experience working with **dynamic forms, state management (Redux / React Hook Form), and complex data-driven interfaces**. I enjoy solving real-world problems by turning ideas into reliable software that companies can actually use in their daily operations. Beyond coding, I care about **software quality and architecture**, following best practices for componentization, code organization, and performance optimization. I'm also comfortable working across the stack when needed, integrating APIs, handling business logic, and helping transform prototypes into production-ready systems. My goal is always to deliver solutions that are **simple, efficient, and genuinely useful for the people using them.** Franck Plazanet Franck Plazanet I am a Strategic Engineering Leader with over 8 years of experience building high-availability enterprise systems and scaling high-performing technical teams. My focus is on bridging the gap between complex technology and business growth. Core Expertise: 🚀 Leadership: Managing and coaching teams of 15+ engineers, fostering a culture of accountability and continuous improvement. 🏗️ Architecture: Enterprise Core Systems, Multi-system Integration (ERP/API/ETL), and Core Database Structure. ☁️ Cloud & Scale: AWS Expert; architected systems handling 10B+ monthly requests and managing 100k+ SKUs. 📈 Business Impact: Aligning tech strategy with P&L goals to drive $70k+ in monthly recurring revenue. I thrive on "out-of-the-box" thinking to solve complex technical bottlenecks and am always looking for ways to use automation to improve business productivity. rayush33 rayush33 JavaScript (React.js, React Native, Node.js) Developer with demonstrated industry experience of 4+ years, actively looking for opportunities to hone my skills as well as help small-scale business owners with solutions to technical problems Anthony Akpan Anthony Akpan Developer with 8 years of experience building softwares fro startups Yovel Cohen Yovel Cohen I got a lot of experience in building Long-horizon AI Agents in production, Backend apps that scale to millions of users and frontend knowledge as well. legrab legrab I'll fill this later Omar Faruk Omar Faruk As a Product Engineer at Klasio, I contributed to end-to-end product development, focusing on scalability, performance, and user experience. My work spanned building and refining core features, developing dynamic website templates, integrating secure and reliable payment gateways, and optimizing the overall system architecture. I played a key role in creating a scalable and maintainable platform to support educators and learners globally. I'm enthusiastic about embracing new challenges and making meaningful contributions. BurnHavoc BurnHavoc Been around fixing other peoples code for 20 years. David Olverson David Olverson Solo dev shipping production apps with AI-assisted development. I specialize in rescuing broken Lovable/Bolt/Cursor builds and taking them to production. 10+ apps shipped including SaaS CRMs, gaming platforms, real estate tools, and Discord bots. Stack: Next.js 16, TypeScript, Tailwind CSS, FastAPI, PostgreSQL, Prisma. I use Claude Code with 50+ custom skills for rapid delivery. Average turnaround: 2-4 weeks from broken prototype to production.

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Frequently Asked Questions

What should I test first when coverage is low?

Prioritize by risk: payment processing, authentication and authorization, data mutations that can't be undone, and any code that handles money or personal data. These are the paths where bugs cause the most damage.

How do I test code that calls external APIs?

Use the service's test mode (Stripe test keys, SendGrid sandbox) for integration tests. Use recorded HTTP responses (nock, VCR, responses) for unit tests. Test both success and error responses from the API.

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