What happens to features that fail the relevant Apex tests during deployment?

Features that fail the relevant Apex tests during a deployment are not deployed. In the context of Salesforce and the deployment process, Apex tests are crucial for ensuring that code changes do not introduce errors or fail to meet business requirements. The deployment will only succeed if all tests pass as they validate the integrity and functionality of the features being deployed.

This restriction helps maintain the stability and reliability of the production environment. By ensuring that only code that has been verified through successful tests is deployed, organizations can avoid unexpected behavior or issues post-deployment. It emphasizes the significance of testing in the development lifecycle and reinforces best practices in software development.