Mockito: mocking an arraylist that will be looped in a for loop

Question

I have a method under test that contains the following snippet: ``` private void buildChainCode(List lines){ for(TracedPath path : lines){ /.../ } } ``` My unit test code looks like this: ``` public class ChainCodeUnitTest extends TestCase { private @Mock List listOfPaths; private @Mock TracedPath tracedPath; protected void setUp() throws Exception { super.setUp(); MockitoAnnotations.initMocks(this); } public void testGetCode() { when(listOfPaths.get(anyInt())).thenReturn(tracedPath); ChainCode cc = new ChainCode(); cc.getCode(listOfPaths); /.../ } } ``` The problem is, that while running the test, the test code never enters the for loop. What when conditions should I specify, so that the for loop would be entered? Currently I have specified `when(listOfPaths.get(anyInt())).thenReturn(tracedPath)`, but I guess it is never used.

Accepted Answer

Your problem is that when you use a collection in a for-each loop, its `iterator()` method gets called; and you haven't stubbed that particular method.

Instead of mocking the list, I strongly recommend you just pass a real list, where the elements are just your mocked `TracedPath`, as many times as you want it. Something like

```
listOfPaths = Arrays.asList(mockTracedPath, mockTracedPath, mockTracedPath);
```

Mockito: mocking an arraylist that will be looped in a for loop

Solution

Problem