public PDFMergerUtility()
    {
        sources = new ArrayList<>();
    }
@Test
    void testPDFMergerUtility() throws IOException
    {
        checkMergeIdentical("PDFBox.GlobalResourceMergeTest.Doc01.decoded.pdf",
                "PDFBox.GlobalResourceMergeTest.Doc02.decoded.pdf",
                "GlobalResourceMergeTestResult1.pdf", 
                IOUtils.createMemoryOnlyStreamCache());
        
        // once again, with scratch file
        checkMergeIdentical("PDFBox.GlobalResourceMergeTest.Doc01.decoded.pdf",
                "PDFBox.GlobalResourceMergeTest.Doc02.decoded.pdf",
                "GlobalResourceMergeTestResult2.pdf", 
                IOUtils.createTempFileOnlyStreamCache());
    }