The difference between unit test/integration test/System test

Unit tests:
Unit testing is a test of the correctness of a software's basic constituent unit (the smallest unit of software design), such as a function, a process (function,procedure), or a method of a class.

Integration testing:
Integration testing is based on unit testing, which assembles all modules into subsystems or systems according to the outline design requirements, verifying that post-assembly functions and the interface between modules are properly tested. Integration testing is also called assembly testing, joint testing, subsystem testing, or component testing.

System test:
System testing is the integration of software systems, as a whole computer system-based elements, and computer hardware, peripherals, some supporting software, data and personnel and other system elements, in the actual use of the environment, the computer system to carry out a series of assembly testing and validation testing work.

Testing phase	Test method	Test method	Assessment Benchmarks	corresponding phase
Unit Test	White box test	Data structure inside the unit, logic control, exception handling, etc.	Logical coverage	Detailed set
Integration Testing	Grey Box test	The overall function of the interface between modules and the combination of modules	Interface coverage	Overview
System Testing	Black box test	Compliance of the entire system to requirements	Test case coverage of requirements	Demand

The difference between unit test/integration test/System test