How to use the aiofiles.threadpool.open function in aiofiles

async def test_simple_peek(mode, tmpdir):
    """Test flushing to a file."""
    filename = 'file.bin'

    full_file = tmpdir.join(filename)
    full_file.write_binary(b'0123456789')

    async with aioopen(str(full_file), mode=mode) as file:
        if 'a' in mode:
            await file.seek(0)  # Rewind for append modes.

        peeked = await file.peek(1)

        # Technically it's OK for the peek to return less bytes than requested.
        if peeked:
            assert peeked.startswith(b'0')

            read = await file.read(1)

            assert peeked.startswith(read)

async def test_simple_iteration(mode):
    """Test iterating over lines from a file."""
    filename = join(dirname(__file__), '..', 'resources', 'multiline_file.txt')

    async with aioopen(filename, mode=mode) as file:
        # Append mode needs us to seek.
        await file.seek(0)

        counter = 1

        # The old iteration pattern:
        while True:
            line = await file.readline()
            if not line:
                break
            assert line.strip() == 'line ' + str(counter)
            counter += 1

        await file.seek(0)
        counter = 1

async def test_simple_close_ctx_mgr(mode, buffering, tmpdir):
    """Open a file, read a byte, and close it."""
    filename = 'bigfile.bin'
    content = b'0' * 4 * io.DEFAULT_BUFFER_SIZE

    full_file = tmpdir.join(filename)
    full_file.write_binary(content)

    async with aioopen(str(full_file), mode=mode, buffering=buffering) as file:
        assert not file.closed
        assert not file._file.closed

    assert file.closed
    assert file._file.closed

async def test_simple_read(mode, buffering):
    """Just read some bytes from a test file."""
    filename = join(dirname(__file__), '..', 'resources', 'multiline_file.txt')
    async with aioopen(filename, mode=mode, buffering=buffering) as file:
        await file.seek(0)  # Needed for the append mode.

        actual = await file.read()

        assert b'' == (await file.read())
    assert actual == open(filename, mode='rb').read()

async def test_simple_close(mode, tmpdir):
    """Open a file, read a byte, and close it."""
    filename = 'bigfile.bin'
    content = '0' * 4 * io.DEFAULT_BUFFER_SIZE

    full_file = tmpdir.join(filename)
    full_file.write(content)

    async with aioopen(str(full_file), mode=mode) as file:
        assert not file.closed
        assert not file._file.closed

    assert file.closed
    assert file._file.closed