Implementing SSL/TLS pinning in Node.js applications adds an extra layer of security against MITM attacks and other certificate-related vulnerabilities. It verifies the server's public key or certificate with a locally stored copy, ensuring the authenticity and integrity of the connection. The process involves comparing the public key during the TLS handshake and terminating the connection if there's a mismatch. Proper error handling is crucial to avoid getting locked out in edge cases where a certificate or public key expires or an issuer revokes it. Testing SSL/TLS pinning by simulating attacks, comparing key hashes, and updating certificates or keys is essential to ensure its effectiveness. Storing public keys securely is also vital for maintaining the trust and security of communication channels. By leveraging SSL/TLS pinning, Node.js applications can enhance their overall security, ensuring a reliable and safe user experience.