### Question:
StringUtils { public static String createQuotedStringIfNotNumeric(String str) { if (isEmpty(str)) { return str; } try { Double.parseDouble(str); } catch (NumberFormatException nfe) { 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 testCreateQuotedConstantOptionalNumericNull() { assertNull(StringUtils.createQuotedStringIfNotNumeric(null)); }
@Test public void testCreateQuotedConstantOptionalNumericEmpty() { assertEquals("", StringUtils.createQuotedStringIfNotNumeric("")); }
@Test public void testCreateQuotedConstantOptionalNumericNumber() { assertEquals("-123", StringUtils.createQuotedStringIfNotNumeric("-123")); }
@Test public void testCreateQuotedConstantOptionalNumeric() { assertEquals("\" abc \"", StringUtils.createQuotedStringIfNotNumeric(" abc ")); }