Mokito Useful tips

Mocking a class:  (This will mock the whole class and all the methods in it.)

 A aMock = Mockito.mock(A.class);

 
Mockito.when(aMock.method()).thenReturn(5l);

 
To mock-a-single-method-in-java use Mockito Spy

A a = new A();  ( where  Class A  has two method - method1() and method2() ) 
A aSpy = Mockito.spy(a);
Mockito.when(aSpy.method1()).thenReturn(5l);

call to  aSpy.method2()  will be actual method call to method2 without any mock effect.

Refer : how-to-mock-a-single-method-in-java

 NOTE: When you are mocking a class make sure you use/inject the mock version only.

Mockito provide simple way to pass parameter to a mocked class method:

e.g : aSpy.method(anyInt(), anyString()) 

this is mock for -> a.method(int i, String stg) 

MOCKITO LIMITATION: 

Mockito has a few limitations worth remembering. They are generally technical restrictions, but Mockito authors believe using hacks to work around them would encourage people to write poorly testable code. Mockito cannot:

• mock final classes
• mock enums
• mock final methods
• mock static methods
• mock private methods
• mock hashCode() and equals()