I'm trying to cook up a mock object for the LayerViewPanel class, which will
allow me to test elements of OpenJUMP's rendering system. However, I've
never had a lot of experience writing or using mock objects in unit testing,
and I have run into a couple of challenges. I was hoping I could explain my
situation and then get some help from the other developers.
I'm trying to test one of my RendererFactoryTool implementations, which
basically creates an instance of
com.vividsolutions.workbench.ui.renderer.LayerRenderer wjhen asked by the
RendererFactory. (This is done whenever an instance of
com.vividsolutions.workbench.model.Layer needs to be rendered for the first
time.) The LayerRenderer class requires a LayerViewPanel as one of the
arguments to its constructor. (This makes sense. The renderer needs a
reference to an object that it can paint on.)
When I am unit testing I don't want to pass the LayerRenderer constructor a
real LayerViewPanel, because that means that I have to create all types of
other unnecessary objects for my test. I just want to pass the constructor a
"dumb" LayerViewPanel and see if it gives me back a Renderer. I need a mock
object.
I thought I could do this by simply extending the LayerViewPanel class and
overriding the methods. This presents two problems:
[1] To have a truly dumb object for my test I'd also need to override the
methods of all the classes in the LayerViewPanel's inheritance tree. (Do you
know how many methods JComponent has???) :[
[2] I still have to make a call to super() in the constructor of my mock
object class, which means I've come full circle to the original problem I
was trying to avoid: Calling the constructor of the LayerViewPanel.
the LayerViewPanel class ins't an interface, so I can't just implement its
methods in my mock object class. What is the solution? Do I set up an
alternate com.vividsolutions.workbench.ui package in my unit testing project
in Eclipse and provide my own version of the LayerViewPanel class? (I think
this will work if I don't make any other imports in my project from which I
want to use the real com.vividsolutions.workbench.ui package.)
Is there another, more elegant solution?
Thanks in advance for the help. I'm really scratching my head on this one.
The Sunburned Surveyor
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