Test Methods 
Test methods are parameterless instance methods of Test Classes and are declared using the FOR TESTING addition of the METHODS statement.
In a test method, the test code is generally implemented by calling production sections of the program under specific starting conditions (Fixtures) and checking the results or statuses with the methods of the system class CL_ABAP_UNIT_ASSERT.
All instance methods are flagged as test methods in Global Test Classes by default. However, you can change this under Details.
Note
Test methods should be private, or protected if the methods are inherited. Since test classes implicitly offer friendship to the test driver in the runtime environment, the driver can call them.