### Question:
StringUtils { public static boolean isInteger(String str) { if (str == null || str.length() == 0) return false; return INT_PATTERN.matcher(str).matches(); }  static boolean isBlank(String str); static boolean isEmpty(String str); static boolean isNotEmpty(String str); static boolean isInteger(String str); static int parseInteger(String str); static Map<String, String> parseQueryString(String qs); static String getServiceKey(Map<String, String> ps); static String toQueryString(Map<String, String> ps); static boolean isEquals(String s1, String s2); static boolean isContains(String values, String value); static boolean isContains(String[] values, String value); static boolean isNumeric(String str); static final String[] EMPTY_STRING_ARRAY; }### Answer:
@Test public void isInteger() throws Exception { assertTrue(StringUtils.isInteger("123")); assertTrue(StringUtils.isInteger("123456789")); assertFalse(StringUtils.isInteger("a123")); assertFalse(StringUtils.isInteger("abc")); assertFalse(StringUtils.isInteger("123abc")); }