assertEquals(3, sis.read(buffer));
        assertArrayEquals(new byte[] { 1, 2, 3 }, buffer);
    }

    @Test
    @DisplayName("Available returns remaining bytes in current message")
    void availableReturnsBytesInCurrentMessage() throws IOException {
        // Create message with 4 bytes
        byte[] data = new byte[] { 1, 2, 3, 4 };
        InputStream in = new ByteArrayInputStream(concat(messageHeader(4), data));