### Question:
ELUtils { public static boolean isNumericString(String s) { if (s == null) return false; char[] characters = s.toCharArray(); for (int charIndex = 0; charIndex < characters.length; charIndex++) { char c = characters[charIndex]; if (!Character.isDigit(c) && !((charIndex == 0) && ((c == '-') || (c == '+')) )) { return false; } } return true; } private  ELUtils(); static boolean isNumericString(String s); static boolean isFloatingPointString(String s);  }### Answer:
@Test public void isNumericString_stringWithNumbersOnly_true() { boolean result = ELUtils.isNumericString("23"); assertTrue(result); }
@Test public void isNumericString_stringWithNumbersAndSign_true() { boolean result = ELUtils.isNumericString("-23"); assertTrue(result); }
@Test public void isNumericString_stringWithNotNumbers_false() { boolean result = ELUtils.isNumericString("ff"); assertFalse(result); }