mockito Getting started with mockito Add behaviour to mocked object

Example

Mockito.when(mock.returnSomething()).thenReturn("my val");

mock.returnSomething(); // returns "my val"
mock.returnSomething(); // returns "my val" again
mock.returnSomething(); // returns "my val" again and again and again...

If you want different value on second call you can add wanted return argument to thenReturn method:

Mockito.when(mock.returnSomething()).thenReturn("my val", "other val");

mock.returnSomething(); // returns "my val"
mock.returnSomething(); // returns "other val"
mock.returnSomething(); // returns "other val" again

If you will call method without adding behaviour to mock it will return null:

barMock.mock.returnSomethingElse(); // returns null

In case that mocked method has parameters, you should declarate values too:

Mockito.when(mock.returnSomething("param 1")).thenReturn("my val 1");
Mockito.when(mock.returnSomething("param 2")).thenReturn("my val 2");

mock.returnSomething("param 1"); // returns "my val 1"
mock.returnSomething("param 2"); // returns "my val 2"
mock.returnSomething("param 3"); // returns null

If you don't care about param value you can use Matchers.any():

Mockito.when(mock.returnSomething(Matchers.any())).thenReturn("p1");

mock.returnSomething("param 1"); // returns "p1"
mock.returnSomething("param other"); // returns "p1"

To throw exception use thenThrow method:

Mockito.when(mock.returnSomething()).thenThrow(new Exception());

mock.returnSomething(); // throws Exception