### Question:
StringUtil { public static String fillString(String str, int length, char fillChar, boolean fillLeft) { int len = length - str.length(); StringBuilder sb = new StringBuilder(); for (int i = 0; i < len; i++) sb.append(fillChar); if (fillLeft) return sb.append(str).toString(); else return str + sb.toString(); }  static boolean isEmpty(String str); static String getLeft(String src, int length); static String getRight(String src, int length); static boolean isDigitOnly(String chkStr); static String SQLEscape(String str); static String fillString(String str, int length, char fillChar, boolean fillLeft); static String cEscape(String str); static String cEscape(String str, char quoteChar); static String cEscape(String str, char quoteChar, boolean isWchar); static String lowerFirst(String str); static String upperFirst(String str); static boolean isJavaIdentifier(String str); static int[] splitAsIntArray(String str, String delimiter); static String join(byte[] items, String delimiter); static String join(String[] items, String delimiter); static String join(List<String> items, String delimiter); static StringBuilder appendRepeatedly(StringBuilder result, String str, int times); static StringBuilder appendRepeatedly(StringBuilder result, char c, int times); static String toTrimmedStr(Object o, int len);  }### Answer:
@Test public void testFillString() { assertEquals("12 ", StringUtil.fillString("12", 4, ' ', false)); assertEquals(" 12", StringUtil.fillString("12", 4, ' ', true)); }