public int indexOf(PDPage page)
    {
        SearchContext context = new SearchContext(page);
        if (findPage(context, root))
        {
            return context.index;
        }
        return -1;
    }
@Test
    void negative() throws IOException
    {
        doc = Loader.loadPDF(RandomAccessReadBuffer.createBufferFromStream(
                TestPDPageTree.class.getResourceAsStream("with_outline.pdf")));
        assertEquals(-1, doc.getPages().indexOf(new PDPage()));
    }