@Test
  public void testSquareRoot() {
    final double DELTA = 1e-15;
    a = 0;
    double result = calculator.squareRoot(a);
    Assert.assertEquals(Math.sqrt(a), result, DELTA);

    a = 1;
    result = calculator.squareRoot(a);
    Assert.assertEquals(Math.sqrt(a), result, DELTA);

    a = 25;
    result = calculator.squareRoot(a);
    Assert.assertEquals(Math.sqrt(a), result, DELTA);

    a = 1544646;
    result = calculator.squareRoot(a);
    Assert.assertEquals(Math.sqrt(a), result, DELTA);
  }
 @Test(timeout = 1000)
 public void testSquareRoot() {
   calculator.squareRoot(4);
   assertEquals(2, calculator.getResult());
 }
 @Test
 public void testSquareRootWithNegativeNumber() {
   a = -26665;
   Double result = calculator.squareRoot(a);
   Assert.assertNull(result);
 }