How to make pytest wait for (manual) user action?

Question

We are sucessfully using pytest (Python 3) to run a test suite testing some hardware devices (electronics). For a subset of these tests, we need the tester to change the hardware arrangement, and afterwards change it back. My approach was to use a module-level fixture attached to the tests in question (which are all in a separate module), with two input calls:

@pytest.fixture(scope="module")
def disconnect_component():
    input('Disconnect component, then press enter')
    yield  # At this point all the tests with this fixture are run
    input('Connect component again, then press enter')

When running this, I get OSError: reading from stdin while output is captured. I can avoid this by calling pytest with --capture=no, and have confirmed that my approach works, meaning I get the first query before the test subset in question, and the second one after they have run.

The big drawback is that this deactivates capturing stdin/stderr for the whole test suite, which some of the other test rely on.

I also tried to use capsys.disabled (docs) like this

@pytest.fixture(scope="module")
def disconnect_component(capsys):
    with capsys.disabled():
        input('Disconnect component, then press enter')
        yield  # At this point all the tests with this fixture are run
        input('Connect component again, then press enter')

but when running this I get ScopeMismatch: You tried to access the 'function' scoped fixture 'capsys' with a 'module' scoped request object, involved factories.

Can I make pytest wait for user action in some other way than input? If not, can I disable capturing just for the tests using above fixture?

Answer 1

So, I found a hint by a pytest dev, based on which I basically do what the capsys.disable() function does:

@pytest.fixture(scope="module")
def disconnect_component(pytestconfig):
    capmanager = pytestconfig.pluginmanager.getplugin('capturemanager')

    capmanager.suspend_global_capture(in_=True)
    input('Disconnect component, then press enter')
    capmanager.resume_global_capture()

    yield  # At this point all the tests with this fixture are run

    capmanager.suspend_global_capture(in_=True)
    input('Connect component again, then press enter')
    capmanager.resume_global_capture()

This works flawlessly as far as I can see. Don't forget the in_=True bit.

Edit: From pytest 3.3.0 (I think), capmanager.suspendcapture and capmanager.resumecapture were renamed to capmanager.suspend_global_capture and capmanager.resume_global_capture, respectively.

Answer 2

Maybe it's worth noting that above solution doesn't have to be in a fixture. I've made a helper function for that:

import pytest

def ask_user_input(msg=''):
    """ Asks user to check something manually and answer a question
    """
    notification = "\n\n???\tANSWER NEEDED\t???\n\n{}".format(msg)

    # suspend input capture by py.test so user input can be recorded here
    capture_manager = pytest.config.pluginmanager.getplugin('capturemanager')
    capture_manager.suspendcapture(in_=True)

    answer = raw_input(notification)

    # resume capture after question have been asked
    capture_manager.resumecapture()

    logging.debug("Answer: {}".format(answer))
    return answer

Answer 3

For future reference, if you need to use input with pytest. You can do this in any part of your pytest, setup_class, test_..., teardown_method, etc. This is for pytest > 3.3.x

import pytest

capture_manager = pytest.config.pluginmanager.getplugin('capturemanager')
capture_manager.suspend_global_capture(in_=True)
answer = input('My reference text here')
capture_manager.resume_global_capture()

Answer 4

Solutions that use the global pytest.config object no longer work. For my use case, using --capture=sys together with a custom input() that uses stdin and stdout directly works well.

def fd_input(prompt):
    with os.fdopen(os.dup(1), "w") as stdout:
        stdout.write("\n{}? ".format(prompt))

    with os.fdopen(os.dup(2), "r") as stdin:
        return stdin.readline()