class Calculator {

    public double mul(double firstOperand, double secondOperand) {
        return firstOperand * secondOperand;
    }

}

class CalculatorTest {

    private Calculator mCalculator;

    @Test
  public void mulTwoNumbersZero() {

    double resultMul = mCalculator.mul(2d, 0d);
    assertThat(resultMul, is(equalTo(0d)));

    }

}