@Test(expected = IllegalArgumentException.class)
 public void test_ThrowsExceptionIfNullInput() {
   CaseStatementRunner.callCaseStatement(null);
 }
 @Test
 public void test_DoesNotThrowsExceptionIfValidInput() {
   CaseStatementRunner.callCaseStatement(1);
   CaseStatementRunner.callCaseStatement(2);
 }