TESTNG: TestNextGeneration
TestNG is a UNIT TESTING TOOL.
It was inspired by JUNIT, 
but a little bit more advanced than JUNIT.
TESTNG helps us create certain testing structure 
using its ANNOTATIONS.
@Test @BeforeSuite @AfterSuite@BeforeTest
@AfterTest @BeforeGroups @AfterGroups
@BeforeClass @AfterClass @BeforeMethod
@AfterMethod
JUnit - the most popular unit testing framework for Java.
TestNG - was created as improved alternative for JUnit.
Both of them, targeting unit testing.