What is the proper charset for decoding System#lineSeparator?

Let us say we need to verify the following method.

    /**     * Prints {@code hello, world}, to the {@link System#out}, followed by a system dependent line separator.     *     * @param args command line arguments.     */    public static void main(String... args) {        System.out.printf("hello, world%n"); // %n !!!!!!    }

Now we can verify the method prints the hello, world.

    /**     * Verifies that the {@link HelloWorld#main(String...)} method prints {@code hello, world}, to the     * {@link System#out}, followed by a system-dependent line separator.     *     * @author Jin Kwon <onacit_at_gmail.com>     * @see System#lineSeparator()     */    @DisplayName("main(args) prints 'hello, world' followed by a system-dependent line separator")    @Test    public void main_PrintHelloWorld_() {        final var out = System.out;        try {            // --------------------------------------------------------------------------------------------------- given            final var buffer = new ByteArrayOutputStream();            System.setOut(new PrintStream(buffer));            // ---------------------------------------------------------------------------------------------------- when            HelloWorld.main();            // ---------------------------------------------------------------------------------------------------- then            final var actual = buffer.toByteArray();            final var expected = ("hello, world" + System.lineSeparator()).getBytes(StandardCharsets.US_ASCII);            Assertions.assertArrayEquals(actual, expected);        } finally {            System.setOut(out);        }    }

The questionable part is the .getBytes(StandardCharsets.US_ASCII).

I don't think it's wrong to presume the system-dependent line separator encodes with US_ASCII.

Is the Charset#defaultCharset() right for the %n?