Beginner Guide: Fix Poor Test Coverage for Backend Developers in Agency Using ChatGPT

You are a senior backend engineer with 11 years of experience in digital agency environments, technical interview preparation, and writing developer documentation for client-facing web projects. Help me write technical documentation so I can improve application performance. My situation: Backend language and framework: [e.g., Node.js with Express / Python with Django / PHP with Laravel] Application type: [e.g., client REST API / e-commerce backend / CMS with custom integrations] Poor test coverage symptom: [e.g., no tests exist / only 3 functions have tests / tests exist but do not cover the paths that fail in production] Interview context: [e.g., preparing for a mid-level backend role / technical screen at an agency that asks about testing and documentation / portfolio project that needs documentation before sharing] Performance problem the documentation should address: [e.g., slow database queries with no explanation of why / caching layer that no one understands how to configure / API endpoints with undocumented rate limits] Documentation audience: [e.g., technical reviewer at the interview company / future developer maintaining this project / agency client technical team] Current documentation state: [e.g., no README / README covers installation only / inline comments exist but are inconsistent] Deliver: A project README template filled in for this specific backend project: includes what the application does, how to run it locally in 5 steps, environment variable reference, and a plain-English description of the architecture A test coverage explanation section: a README section that honestly describes the current test coverage state, what is tested, what is not yet tested, and the plan to improve it — written to demonstrate self-awareness rather than hide the gap A performance documentation section: explain the 3 most performance-sensitive parts of the application — what they do, why they are slow, and what the fix or workaround is — written so a technical interviewer understands the developer's reasoning An API endpoint reference: document the 5 most important endpoints with method, path, required parameters, example request, example response, and the most common error response — formatted as a plain-text table a beginner can produce without a Swagger tool A code comment standard: define the 3 types of inline comments needed in this codebase — why a decision was made, what a non-obvious block does, and what a known limitation is — with one example of each written for the specific project A testing roadmap: define the 5 tests to write first to improve test coverage fastest, ordered by the risk of the untested function in a production environment, with a one-sentence description of what each test confirms A technical interview talking points guide: 5 specific things the developer can say about this project's documentation and testing approach during an interview — framed around decisions made, trade-offs accepted, and improvements planned A documentation review checklist: 6 questions to answer before sharing the project with an interviewer — confirming the README is accurate, environment variables are documented, no sensitive data is exposed, and the performance section reflects the actual codebase Write the README before preparing interview talking points — an interviewer who reads documentation before the call forms an impression that the conversation either confirms or contradicts. Make the documentation do the first round of convincing.