counter in smartpy

counter.py

import smartpy as sp

class Counter(sp.Contract):
  def __init__(self):
    self.init(counter = 0)

  @sp.entryPoint
  def increaseCounterBy(self, params):
    self.data.counter = self.data.counter + params.value

  @sp.entryPoint
  def decreaseCounterBy(self, params):
    self.data.counter = self.data.counter - params.value


if "templates" not in __name__:
  @addTest(name = "Counter test")
  def test():
    c1 = Counter()
    scenario = sp.testScenario()
    scenario += c1
    scenario += c1.increaseCounterBy(value = 2)
    scenario += c1.decreaseCounterBy(value = 1)
    scenario.verify(c1.data.counter == 1)