Exercise Unit Testing

I have in Java written a Stack object.
It us used by the following code:

private StackDouble MyDoubleStack = new StackDouble();		
MyDoubleStack.empty()
MyDoubleStack.pop();
MyDoubleStack.push(variableName);

Group work:
In your small group, come up with a plan for Unit Testing, to make sure the stack actually works as advertised, so that it can be used by other routines.

Individual work:
The stack is called from my calculator object.
It simulates a calculator, of course.

Come up with a plan for testing the calculator object, which calls the StackDouble object.
(It also calls the StackChar object.) 
The goal is to make sure that the calculator object calls/uses the stack object correctly.
Your plan should NOT count on the stack object working correctly.
(Why not?)