### Question:
StringUtils { public static String createQuotedString(final String str) { if (isEmpty(str)) { return str; } return "\"" + str + "\""; } private  StringUtils(); static boolean isEmpty(final String s); static boolean nonEmpty(final String s); static boolean hasNonEmpty(final String... values); static boolean isQuoted(String str); static String createQuotedString(final String str); static String createQuotedStringIfNotNumeric(String str); static String replaceIllegalCharsAttribute(final String value); static String replaceIllegalCharsForDataObjects(final String value); static String revertIllegalCharsAttribute(final String value); static String createUnquotedString(String str);  }### Answer:
@Test public void testCreateQuotedConstantNull() { assertNull(StringUtils.createQuotedString(null)); }
@Test public void testCreateQuotedConstantEmpty() { assertEquals("", StringUtils.createQuotedString("")); }
@Test public void testCreateQuotedConstantNumber() { assertEquals("\"-123\"", StringUtils.createQuotedString("-123")); }
@Test public void testCreateQuotedConstant() { assertEquals("\" abc \"", StringUtils.createQuotedString(" abc ")); }