@Test
 public void testMultiply() throws Exception {
   assertEquals(
       HTTPRequestTestHelper.getResponse("http://localhost:8080/calc/multiply?a=13&b=3"), "39");
 }
 @Test
 public void testAdd() throws Exception {
   assertEquals(
       HTTPRequestTestHelper.getResponse("http://localhost:8080/calc/add?a=13&b=3"), "16");
 }
 @Test
 public void testSubstract() throws Exception {
   assertEquals(
       HTTPRequestTestHelper.getResponse("http://localhost:8080/calc/substract?a=13&b=3"), "10");
 }
 @Test
 public void testDivide() throws Exception {
   assertEquals(
       HTTPRequestTestHelper.getResponse("http://localhost:8080/calc/divide?a=33&b=3"), "11");
 }