Definitions

Unit test

A unit test tests the smallest testable part of an application (a unit). For our purposes, this is a function.

Integration test

An integration test combines two or more individual units and tests them as a group.

End-to-end test

An end-to-end test tests a flow from start to end and validates different integrated components of an application.

End-to-end Testing tests the integrity of the integrated components as well as the integrity of the whole system.

System testing

A system test tests a complete, integrated system as a whole to evaluate the system's compliance with its specified requirements.

System testing falls within the scope of black-box testing, and as such, should require no knowledge of the inner design of the code or logic.