Add tests for new terminal and editor handling

[afshin]

cf. #31

This is a test that was removed from jupyter_server that should be included in nbclassic:

"""Basic tests for the notebook handlers.
"""

import asyncio
import json
import pytest

async def test_terminal_create_with_cwd(
    fetch,
    ws_fetch,
    terminal_path,
    kill_all
):
    resp = await fetch(
        'api', 'terminals',
        method='POST',
        body=json.dumps({'cwd': str(terminal_path)}),
        allow_nonstandard_methods=True,
    )

    data = json.loads(resp.body.decode())
    term_name = data['name']

    ws = await ws_fetch(
        'terminals', 'websocket', term_name
    )
    await ws.write_message(json.dumps(['stdin', 'pwd\r']))

    messages = ""
    while True:
        try:
            response = await asyncio.wait_for(ws.read_message(), timeout=1.0)
        except asyncio.TimeoutError:
            return messages

        response = json.loads(response)
        if response[0] == "stdout":
            messages += response[1]

    ws.close()
    assert str(terminal_path) in messages
    await kill_all()