Pytest: Mocking STDIN manually mocking

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examples/pytest/stdin/test_one.py

import app
import io
import sys

def test_app(capsys):
    sys.stdin = io.StringIO('Foo')
    app.ask_one()
    out, err = capsys.readouterr()
    assert err == ''
    #print(out)
    assert out == 'Please enter your name: Your name is Foo\n'

def test_app_again(capsys):
    ...   # still the same handle

examples/pytest/stdin/test_two.py

import app
import io
import sys

def test_app(capsys):
    sys.stdin = io.StringIO('3\n4')
    app.ask_two()
    out, err = capsys.readouterr()
    assert err == ''
    #print(out)
    assert out == 'Please enter width: Please enter length: 3.0*4.0 is 12.0\n'