All have those test nouns. __ Test

Unit Testing , is to focus on the source code to achieve each of the program units to test, check whether each program module correctly implemented the specified function. The integrated test assembles the tested modules and tests the structure of the software architecture related to the design. The system test incorporates the validated software into the actual operating environment and tests with other system components.
Unit Test (unit testing)

Unit test, also known as module testing, is a software design of the smallest unit-program module, the test of correctness test. The aim is to find all kinds of errors that may exist within each module. Unit tests need to design test cases from the internal structure of the program. Multiple modules can be unit tested independently of each other.
Integration testing (Integrated testing)
Generally, on the basis of unit testing, all modules need to be assembled into the system according to the design requirements. The issues to consider at this point are:
-whether the data passing through the module interface will be lost when the modules are connected;
– Whether the functionality of one module adversely affects the functionality of another module;
-Each child function can be combined to achieve the desired parent function;
– Global data structures are problematic;
– The error of a single module accumulates and is magnified to an unacceptable level.
At the same time unit test can carry on the integration test, discovers and eliminates the problem which may appear in the module connection, finally constitutes the request software system. subsystem integration testing is especially known as component testing, and it does work to identify inconsistencies between integrated subsystems and system requirements specifications.

Systems Testing (System testing)

System test, is to confirm the test software, as an entire computer-based system element, and computer hardware, peripherals, some support software, data and personnel and other system elements together, in the actual operating environment, the computer system to carry out a series of assembly tests and validation tests. The purpose of system testing is to find out where the definition of software and system is inconsistent or inconsistent with the requirements definition of the system.

Acceptance test I (UAT)