// Create a minimal valid security descriptor binary
        // Format: revision(1) + sbz1(1) + control(2) + ownerOffset(4) + groupOffset(4) + saclOffset(4) + daclOffset(4) = 20 bytes minimum
        byte[] securityDescriptorBytes = new byte[20];
        securityDescriptorBytes[0] = 1; // revision
        securityDescriptorBytes[1] = 0; // sbz1
        // control flags (2 bytes)
        securityDescriptorBytes[2] = 0;

        response = spy(response);
        when(response.getHeaderStart()).thenReturn(0);

        // Write minimal SecurityDescriptor header (20 bytes)
        buffer[20] = 1; // Revision
        buffer[21] = 0; // Sbz1
        SMBUtil.writeInt2(0x8004, buffer, 22); // Control flags
        SMBUtil.writeInt4(0, buffer, 24); // Owner offset
        SMBUtil.writeInt4(0, buffer, 28); // Group offset

        StringBuilder sb1 = new StringBuilder("first");
        StringBuilder sb2 = new StringBuilder("second");
        String result = StringUtil.join(",", sb1, sb2);
        assertEquals("first,second", result);
    }

    @Test
    @DisplayName("Should handle StringBuffer as CharSequence")
    void testJoinWithStringBuffer() {
        StringBuffer sb1 = new StringBuffer("alpha");