Challenge made by @coreyhaines on the http://kickstartacademy.io podcast.

stack.rb

class Stack
  def empty?
    true
  end
  def push(element)
    @empty = false
  end
end

def assert(expected, actual, msg="FAIL!")
  if expected != actual
    raise "Failed test. #{expected} should have been #{actual}"
  end
end

# a new stack is empty
s = Stack.new
assert(true, s.empty?)

# a stack is not empty after I push
s = Stack.new
s.push 5
if false != s.empty?
  raise "Stack should not have been empty"
end