verifyNoMoreInteractions(renewable);
    }

    @Test
    @DisplayName("Edge: calling renew() on a null reference throws NPE")
    void renewOnNullReferenceThrowsNPE() {
        // Arrange: null reference to the interface
        SmbRenewableCredentials creds = null;

        // Act + Assert: invoking renew() on null triggers NullPointerException