When working with environment variables for configuration: 1. **Reuse existing environment variables** rather than creating new ones. Leverage established variables like `NODE_TEST_CONTEXT` where possible to avoid fragmentation. 2. **Extract only necessary environment variables** instead of passing the entire environment. This improves security and makes dependencies explicit. ```javascript // Avoid: proxyEnv: process.env.NODE_USE_ENV_PROXY ? process.env : undefined, // Prefer: proxyEnv: process.env.NODE_USE_ENV_PROXY ? { HTTP_PROXY: process.env.HTTP_PROXY, HTTPS_PROXY: process.env.HTTPS_PROXY, NO_PROXY: process.env.NO_PROXY } : undefined, ``` 3. **Check environment variables consistently** and be mindful of truthiness. Remember that environment variables are strings or undefined, and plan accordingly. 4. **Document new environment variables** if you absolutely must create them, and ensure they follow established naming conventions for your project.