* Tests the append method of the DfsReferral class.
     * It verifies that a new DfsReferral object can be successfully appended to an existing one,
     * forming a linked list structure.
     */
    @Test
    void testAppend() {
        // Given
        DfsReferral initialReferral = new DfsReferral();
        DfsReferral appendedReferral = new DfsReferral();

        // When
        initialReferral.append(appendedReferral);