public boolean replaceExtension(String text) {
        int pt = text.indexOf(this.OLDEXT);
        if (pt > -1) {
            int extsize = this.OLDEXT.length();
            this.NEWFILE = text.substring(0, pt) + this.NEWEXT + text.substring(pt + extsize);
            return true;
        } else {
            return false;
        }
    }
@Test
    public void testReplaceExtension() {
        testf.setReplaceExtension("html", "jsp");
        testf.isFiltered(TESTSTR, null);// set the required variables
        Assertions.assertEquals(TESTSTROUT, testf.filter(TESTSTR));
    }