### Question:
Calculator { public double subtraction(double firstOperand, double secondOperand) { return firstOperand - secondOperand; }  double addition(double firstOperand, double secondOperand); double subtraction(double firstOperand, double secondOperand); double division(double firstOperand, double secondOperand); double multiplication(double firstOperand, double secondOperand);  }### Answer:
@Test public void subTwoNumbers(){ double resultSub = mCalculator.subtraction(2d, 1d); assertThat(resultSub, is(equalTo(1d))); }
@Test public void subWorksWithNegativeResults(){ double resultSub = mCalculator.subtraction(2d, 10d); assertThat(resultSub, is(equalTo(-8d))); }