* @param fieldName the field name for error reporting
     * @return the validated string
     * @throws IllegalArgumentException if string is null or empty
     */
    public static String requireNonEmpty(String value, String fieldName) {
        if (value == null) {
            throw new IllegalArgumentException(fieldName + " cannot be null");
        }
        if (value.trim().isEmpty()) {

        assertEquals("test", InputValidator.requireNonEmpty("test", "field"));

        assertThrows(IllegalArgumentException.class, () -> InputValidator.requireNonEmpty(null, "field"));
        assertThrows(IllegalArgumentException.class, () -> InputValidator.requireNonEmpty("", "field"));
        assertThrows(IllegalArgumentException.class, () -> InputValidator.requireNonEmpty("   ", "field"));
    }

    @Test