@Test
  public void test_pi_subtract() {
    double result = MathLib.subtract(8, MathLib.getPI());
    double expected = 4.858407346410207;

    assertEquals(expected, result, 0.00001);
  }
 @Test
 public void test_subtraction_failed() {
   MathLib calc = new MathLib();
   double result = calc.subtract(1, 5);
   double expected = 4;
   assertEquals(expected, result, 0.00001);
 }