As a future or present software tester you need to know the theoretical aspects of a testing. Now were going to describe 4 testing levels which you need to know and understand.
Unit testing — this is a testing of one individual module or a source code and usually it’s made by developers. This type of testing helps to find mistakes in code and fix them before module will be send to deployment.
Integration testing — in this level we test group of modules and how they interact with each other. For example login module and account module. There are different approaches as Big Bang, Top Down, Bottom Up, Sandwich testing, Risky — hardest.
System testing — this is a testing of entire system and how it interacts with other systems. For example balance module need to work with transfer module exactly as it’s writen in SRS (software requirement specification).
Acceptance testing — level of software testing when we test product to know whether it meets clients needs and expectations or not. All the requirements are gathered in software requirement specification and we can test through it step by step.