InputStream s = new ByteArrayInputStream(new byte[] { 0x1F });
        int tagNo = ASN1Util.readTagNumber(s, 0x1F);
        assertEquals(31, tagNo);
    }

    @Test
    void testReadTagNumber_MultiByte() throws IOException {
        // Multi-byte tag (e.g., 80)
        InputStream s = new ByteArrayInputStream(new byte[] { (byte) 0x81, 0x00 });
        int tagNo = ASN1Util.readTagNumber(s, 0x1F);