How to test using JUnit4 when there is @InjectComponent

[newbie newbie]

Hi,
**

I am testing using Junit4 with eclipse. I want to test the function
expandAll

public void expandAll(TreeExpansionModel<TreeData> expansionModel)
{
    List<TreeNode<TreeData>> roots = getTreeModel().getRootNodes();
    for (TreeNode<TreeData> root : roots)
    {
        expandAllNode(root, expansionModel);
    }
}

private void expandAllNode(TreeNode<TreeData> node,
TreeExpansionModel<TreeData> expansionModel)
{
       if (node.getHasChildren())
      {
          expansionModel.markExpanded(node);
          for (TreeNode child : node.getChildren())
         {
             expandAllNode(child, expansionModel); // this is a recursive
call
          }
       }
}



The problem I am having is the expansionModel. In my program(not test), I
pass in the expansionModel using tree. Here is the code fragment from java.

@InjectComponent
private Tree tree;

public void onExpandAll()
{
     expansionModel = tree.getExpansionModel();
     treeFunction.expandAll(expansionModel);

     ajaxResponseRenderer.addRender(treeZone);

}

I have tried in my test using

tree = new Tree();
expansionModel = tree.getExpansionModel();
testing.expandAll(expansionModel);

but the expansionModel I get is null. How do I go about testing with
@InjectComponent tree? Any help would be appreciated. Thanks.