What is a testing hierarchy?

^Unit testing: Developers test their code to make sure the functionality they created is working. ^Component Testing: Component is a standalone functionality that can work by itself ^Integration Testing: All modules are combined. When integrated do they still work together ^System Testing: Hardware, Software, Database, servers everything ^Acceptance Testing: (User Acceptance Testing). It's testing done by a UAT team mostly business/client-side team or hired UAT team that validates what QA team tested before moving to production.