@Test
  public void test_pi_multiply() {
    double result = MathLib.multiply(5, MathLib.getPI());
    double expected = 15.707963267948966;

    assertEquals(expected, result, 0.00001);
  }
  @Test
  public void test_pi_divide() {
    double result = MathLib.divide(5, MathLib.getPI());
    double expected = 1.5915494309189535;

    assertEquals(expected, result, 0.00001);
  }
  @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_pi_add() {
    double result = MathLib.add(5, MathLib.getPI());
    double expected = 8.141592653589793;

    assertEquals(expected, result, 0.00001);
  }
  @Test
  public void test_pi_failed() {
    double result = MathLib.getPI();
    double expected = 3.14;

    assertEquals(expected, result, 0.00001);
  }
  @Test
  public void test_pi_square() {
    double result = MathLib.squareRoot(MathLib.getPI());
    double expected = 1.7724538509055159;

    assertEquals(expected, result, 0.00001);
  }