pexpect tests hang on macOS

[jaraco]

In #985, I discovered that many tests on macOS are bypassed because pexpect appears to operate unreliably on that platform.

[jaraco]

I found that even consuming all of the input before calling .wait() doesn't stop the block forever behavior. But if instead I do something like the following, it causes child.isalive() to return False and the test to pass.

diff -r 1d9397a85c2c testing/test_pdb.py
--- a/testing/test_pdb.py   Fri Oct 21 01:36:24 2016 +0200
+++ b/testing/test_pdb.py   Fri Oct 21 12:01:25 2016 -0400
@@ -141,10 +141,20 @@
         child = testdir.spawn_pytest("--pdb %s" % p1)
         #child.expect(".*import pytest.*")
         child.expect("(Pdb)")
+        print("got here 1")
         child.sendeof()
+        print("got here 2")
         child.expect("1 error")
+        print("got here 3")
+        while True:
+            try:
+                child.read_nonblocking()
+            except Exception:
+                break
         if child.isalive():
+            print("got here 6")
             child.wait()
+        print("got here 5")

     def test_pdb_interaction_on_internal_error(self, testdir):
         testdir.makeconftest("""
$ python -m tox -e py35 -- -s -k test_pdb_interaction_on_collection_issue181 -v
GLOB sdist-make: /Users/jaraco/Dropbox/code/public/pytest/setup.py
py35 inst-nodeps: /Users/jaraco/Dropbox/code/public/pytest/.tox/dist/pytest-3.0.4.dev0.zip
py35 installed: hypothesis==3.5.3,mock==2.0.0,nose==1.3.7,pbr==1.10.0,pexpect==4.2.1,ptyprocess==0.5.1,py==1.4.31,pytest==3.0.4.dev0,requests==2.11.1,six==1.10.0,spark-parser==1.4.0,uncompyle6==2.9.2,xdis==3.1.0
py35 runtests: PYTHONHASHSEED='1622146962'
py35 runtests: commands[0] | pytest --lsof -rfsxX -s -k test_pdb_interaction_on_collection_issue181 -v
=========================================== test session starts ===========================================
platform darwin -- Python 3.5.2, pytest-3.0.4.dev, py-1.4.31, pluggy-0.4.0 -- /Users/jaraco/Dropbox/code/public/pytest/.tox/py35/bin/python3.5
cachedir: .cache
rootdir: /Users/jaraco/Dropbox/code/public/pytest, inifile: tox.ini
plugins: hypothesis-3.5.3
collected 1724 items 

testing/test_pdb.py::TestPDB::test_pdb_interaction_on_collection_issue181 got here 1
got here 2
got here 3
got here 5
PASSED

========================================== 1723 tests deselected ==========================================
================================ 1 passed, 1723 deselected in 2.42 seconds ================================
_________________________________________________ summary _________________________________________________
  py35: commands succeeded
  congratulations :)

[brianmaissy]

Reappeared in test_pdb_custom_cls_with_settrace in d75748e, I'll open a PR

[zakkg3]

Happened to me today.

Darwin 18.7.0 Darwin Kernel Version 18.7.0: Tue Aug 20 16:57:14 PDT 2019; root:xnu-4903.271.2~2/RELEASE_X86_64 x86_64
python --version Python 3.7.4

Calling ssh-keygen was hanging on .wait() : this was working in linux
Solved by read_nonblocking() and if isalive() wait()

import os
import sys

import pexpect


passphrase = os.environ['HOST_CA_KEY_PASSPHRASE']

command = 'ssh-keygen'
child = pexpect.spawn(command, args=sys.argv[1:])
child.expect('Enter passphrase:')
child.sendline(passphrase)

# Avoid Hang on macOS
# https://github.com/pytest-dev/pytest/issues/2022
while True:
    try:
        child.read_nonblocking()
    except Exception:
        break

if child.isalive():
    child.wait()

[blueyed]

@zakkg3
This issue is about tests in pytest itself..

IIRC it will hang on osx with unread output.

Maybe the pytester spawn method could take care of that automatically? (i.e. read anything on test/fixture teardown)?