Bug: PosixCommands.tail counts newlines rather than lines

[freva]

PosixCommands.tail -n N returns one more line than requested when the input does not end with a newline character. The implementation counts newline characters rather than lines.

@TempDir
Path tempDir;

@Test
void tail_noTrailingNewline_returnsOneExtraLine() throws Exception {
    String input = "a\nb\nc\nd\ne";
    String actual = runTail(input, "tail", "-n", "2");
    assertEquals("d\ne", actual); // Fails, returns "c\nd\ne" instead of "d\ne"
}

@Test
void tail_withTrailingNewline_returnsCorrectLines() throws Exception {
    String input = "a\nb\nc\nd\ne\n";
    String actual = runTail(input, "tail", "-n", "2");
    assertEquals("d\ne\n", actual); // Fails, returns "d\ne" instead of "d\ne\n"
}

private String runTail(String input, String... args) throws Exception {
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    InputStream in = new ByteArrayInputStream(input.getBytes(StandardCharsets.UTF_8));
    try (DumbTerminal terminal = new DumbTerminal(in, out)) {
        PosixCommands.Context ctx = new PosixCommands.Context(
                in,
                new PrintStream(out),
                new PrintStream(new ByteArrayOutputStream()),
                tempDir,
                terminal,
                k -> null);

        PosixCommands.tail(ctx, args);
    }
    return out.toString(StandardCharsets.UTF_8).trim();
}

[freva]

Piped content is trimmed, so piping a file that ends in a newline to tail ends up with content without newline.