assertEquals("First line", "Line number 0", receivedLines.get(0));
        assertEquals("Last line", "Line number 4999", receivedLines.get(4999));
    }

    public void test_run_concurrentAccess() throws InterruptedException {
        String input = "concurrent1\nconcurrent2\nconcurrent3";
        InputStream is = new ByteArrayInputStream(input.getBytes(StandardCharsets.UTF_8));