input: Write a function to test the 'add' and 'subtract' methods of the Calculator class.
  assert calc.values == [5, -1]
output: def test_calculator_operations():
      class Calculator:
          def __init__(self):
              self.values = []
          
          def add(self, value):
              self.values.append(value)
          
          def subtract(self, value):
              self.values.append(-value)
      
      calc = Calculator()
      calc.add(5)
      calc.subtract(1)
      assert calc.values == [5, -1]