temp2.rb

describe Stack do

  # Suggested Syntax...
  Invariants do
    If { stack.empty? }
    Then { stack.depth.should == 0 }
    Then { stack.should be_pushable }
    ElseIf { stack.full? }
    Then { stack.depth.should == stack.max_depth }
    Then { stack.should_not be_pushable }
    Else
    Then { stack.depth.should be > 0 } # not wild about this part
  end

  # all of the above can be done with existing invariants
  # (and an imply matcher)

  Invariant { stack.empty?.should imply(stack.depth == 0) }
  Invariant { stack.empty?.should imply(stack.pushable?) }
  Invariant { stack.full?.should imply(stack.depth == stack.max_depth) }
  Invariant { stack.full?.should imply(! stack.pushable?) }
  Invariant { (!stack.full? && ! stack.empty?).should imply(stack.depth > 0) }

end