Prompt test with backspace+validator

Hi,

I try to setup unit tests on some code based on prompt. But i am not able to write backspace to the input stream with validator. It sounds like after the first \n aborted by the validator, the \b behave like a left arrow key.

I don't have such behaviour outside of the unittest.

from prompt_toolkit.shortcuts import PromptSession
from prompt_toolkit.input import create_pipe_input
from prompt_toolkit.output import DummyOutput
from prompt_toolkit.validation import Validator, ValidationError


def test_prompt_session():
    """Copy paste of the example provided by prompt toolkit + backspace"""
    with create_pipe_input() as inp:
        inp.send_text("hello\b\n")
        session = PromptSession(
            input=inp,
            output=DummyOutput(),
        )

        result = session.prompt()

    assert result == "hell"


def test_prompt_session2():
    class NameValidator(Validator):
        def validate(self, document):
            text = document.text.lower()
            if not text.isidentifier():
                raise ValidationError(
                    message="The input must be an identifier"
                )

    with create_pipe_input() as inp:
        session = PromptSession(
            input=inp,
            output=DummyOutput(),
            validator=NameValidator()
        )
        inp.send_text("1t\n\b\ba\n")

        result = session.prompt()

    assert result == "a"

The result it

>       assert result == "a"
E       AssertionError: assert 'a1t' == 'a'
E         - a
E         + a1t

Do you have any idea what's wrong or how i should check such key sequence?

Start with the two test cases using PromptSession, create_pipe_input, DummyOutput, and the validator, then trace how the input sequence is handled after validation fails. Reproduce the behavior with 1t\n\b\ba\n and compare it with hello\b\n; done means the validated sequence returns a while the non-validator case still returns hell.