@Test
        @DisplayName("toString with null challenge throws NPE")
        void testToStringWithNullChallengeThrowsNPE() {
            UniAddress dc = mock(UniAddress.class);
            when(dc.toString()).thenReturn("ANYSERVER");

            NtlmChallenge nc = new NtlmChallenge(null, dc);

            // Hexdump.toHexString will throw NPE when accessing challenge.length

    }

    /**
     * Ensure encode throws NPE when passed a null buffer.
     */
    @Test
    @DisplayName("Encode with null buffer throws NullPointerException")
    public void testEncodeNullBuffer() throws NdrException {
        NdrHyper hyper = new NdrHyper(5L);
        assertThrows(NullPointerException.class, () -> hyper.encode(null));
    }

    /**
     * Ensure decode throws NPE when passed a null buffer.
     */
    @Test

        verify(mockDir, times(3)).getPath();
        verifyNoMoreInteractions(mockDir);
    }

    /**
     * Defensive behavior: implementation throws NPE on null inputs by design.
     */
    @Test
    @DisplayName("implementation explicitly rejects nulls with NPE")
    void implementationRejectsNulls() {
        SmbFilenameFilter filter = (dir, name) -> {
            if (dir == null || name == null) {

    }

    // Invalid input: null reqPath leads to NPE from implementation
    @Test
    @DisplayName("handleDFSReferral throws NPE on null reqPath")
    void handleDfsReferralNullPathThrows() {
        when(locator.handleDFSReferral(any(), isNull())).thenThrow(new NullPointerException("reqPath"));
        NullPointerException npe = assertThrows(NullPointerException.class, () -> locator.handleDFSReferral(referral, null));

        // Constructor accepts null principal without throwing exception
        NtlmHttpServletRequest request = new NtlmHttpServletRequest(mockRequest, null);

        // getRemoteUser() will throw NPE when trying to call getName() on null principal
        assertThrows(NullPointerException.class, () -> request.getRemoteUser());
        assertNull(request.getUserPrincipal());
        assertEquals("NTLM", request.getAuthType());

    @Mock
    private Configuration mockConfig;

    private SmbComSetInformationResponse response;

    @BeforeEach
    void setUp() {
        // Setup mock configuration to avoid NPE
        when(mockConfig.getPid()).thenReturn(12345);

        response = new SmbComSetInformationResponse(mockConfig);
    }

    @Test
    @DisplayName("Constructor accepts valid config")

            assertEquals("Named pipes are only valid on IPC$", ex.getMessage());
        }

        @Test
        @DisplayName("Null context throws NPE (invalid input)")
        void nullContextThrows() {
            assertThrows(NullPointerException.class, () -> new SmbNamedPipe("smb://server/IPC$/foo", 0, null));
        }

        @Test

        assertThrows(NoSuchMethodException.class, () -> SessionSetupHandler.class.getDeclaredConstructor());
    }

    @Test
    @DisplayName("Invalid: resolving class by null name throws NPE")
    void testClassForNameWithNull() {
        // Intent: demonstrate defensive behavior with null when resolving this type by name
        assertThrows(NullPointerException.class, () -> Class.forName(null));
    }

    }

    // --- Invalid/null usage: calling a method on null should throw NPE ---
    @Test
    void nullReference_throwsNullPointerException() {
        // Arrange
        SmbBasicFileInfo info = null;

        // Act & Assert: attempting to call any method on null should throw NPE
        Assertions.assertThrows(NullPointerException.class, () -> {

            }
            return true; // not reached in this test
        };

        // Act + Assert
        NullPointerException npe = assertThrows(NullPointerException.class, () -> filter.accept(null));
        assertEquals("file must not be null", npe.getMessage());
    }