Cursor is the strongest fit here because it works directly inside your editor, can read your existing codebase, and will generate test files that match your project's language, framework, and conventions with minimal setup. You paste or open the untested code, describe what you need, and it produces unit or integration tests you can run immediately. Claude Sonnet is a solid alternative when you want to paste code into a chat and get a thorough explanation of testing strategy alongside the generated tests. Deepseek Coder is worth considering if you want a free option that is specifically tuned for code tasks. GitHub Copilot fits well if you prefer a lighter inline suggestion flow rather than a full agentic session.