Calculator { public double sub(double firstOperand, double secondOperand) { return firstOperand - secondOperand; }  double add(double firstOperand, double secondOperand); double sub(double firstOperand, double secondOperand); double div(double firstOperand, double secondOperand); double mul(double firstOperand, double secondOperand); double pow(double firstOperand, double secondOperand);  }
@Test public void subWorksWithNegativeResult() { double resultSub = mCalculator.sub(1d, 17d); assertThat(resultSub, is(equalTo(-16d))); }
@Test public void subTwoNumbers() { double resultSub = mCalculator.sub(1d, 1d); assertThat(resultSub, is(equalTo(0d))); }
@Test public void subWorksWithNegativeResults() { double resultSub = mCalculator.sub(1d, 17d); assertThat(resultSub, is(equalTo(-16d))); }