Tests fail with weird error if python2 is not installed

[ukch]

Describe the bug
Pipes does not require Python 2 to operate. It should not require it for tests, but at present the tests do not pass unless it is installed.

To Reproduce

• Make sure there is no system python2 executable available
• Run pytest

Expected behavior
The tests should pass

Actual behaviour
Tests fail with an error like the following:

___________ ERROR at setup of TestFindEnvironments.test_find_binary ____________

request = <FixtureRequest for <Function 'test_find_binary'>>

    def fill(request):
        item = request._pyfuncitem
        fixturenames = item.fixturenames
        autousenames = item.session._fixturemanager._getautousenames(item.nodeid)
    
        for fname in fixturenames:
            if fname not in item.funcargs and fname in autousenames:
                item.funcargs[fname] = request.getfixturevalue(fname)
    
        if hasattr(item, 'callspec'):
            for param, val in sorted_by_dependency(item.callspec.params, fixturenames):
                if is_lazy_fixture(val):
                    item.callspec.params[param] = request.getfixturevalue(val.name)
    
>       _fillfixtures()

/usr/lib/python3/dist-packages/pytest_lazyfixture.py:40: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
tests/conftest.py:129: in mock_env_home
    envs = find_environments(pipenv_home)
pipenv_pipes/core.py:33: in find_environments
    binpath = find_binary(envpath)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

envpath = '/tmp/pipenv_home_real0cjax3c0/proj1-7PMzaxDr'

    def find_binary(envpath):
        """ Finds the python binary in a given environment path """
        env_ls = os.listdir(envpath)
        if 'bin' in env_ls:
            binpath = os.path.join(envpath, 'bin', 'python')
        elif 'Scripts' in env_ls:
            binpath = os.path.join(envpath, 'Scripts', 'python.exe')
        else:
            raise EnvironmentError(
>               'could not find python binary path: {}'.format(envpath))
E           OSError: could not find python binary path: /tmp/pipenv_home_real0cjax3c0/proj1-7PMzaxDr

pipenv_pipes/core.py:52: OSError
________ ERROR at setup of TestFindEnvironments.test_get_python_version ________

request = <FixtureRequest for <Function 'test_get_python_version'>>

    def fill(request):
        item = request._pyfuncitem
        fixturenames = item.fixturenames
        autousenames = item.session._fixturemanager._getautousenames(item.nodeid)
    
        for fname in fixturenames:
            if fname not in item.funcargs and fname in autousenames:
                item.funcargs[fname] = request.getfixturevalue(fname)
    
        if hasattr(item, 'callspec'):
            for param, val in sorted_by_dependency(item.callspec.params, fixturenames):
                if is_lazy_fixture(val):
                    item.callspec.params[param] = request.getfixturevalue(val.name)
    
>       _fillfixtures()

/usr/lib/python3/dist-packages/pytest_lazyfixture.py:40: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
tests/conftest.py:129: in mock_env_home
    envs = find_environments(pipenv_home)
pipenv_pipes/core.py:33: in find_environments
    binpath = find_binary(envpath)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

envpath = '/tmp/pipenv_home_realeeyf2spo/proj1-AJFfG1vO'

    def find_binary(envpath):
        """ Finds the python binary in a given environment path """
        env_ls = os.listdir(envpath)
        if 'bin' in env_ls:
            binpath = os.path.join(envpath, 'bin', 'python')
        elif 'Scripts' in env_ls:
            binpath = os.path.join(envpath, 'Scripts', 'python.exe')
        else:
            raise EnvironmentError(
>               'could not find python binary path: {}'.format(envpath))
E           OSError: could not find python binary path: /tmp/pipenv_home_realeeyf2spo/proj1-AJFfG1vO

pipenv_pipes/core.py:52: OSError

After a bit of digging, I managed to trace the problem to the virtualenv creation. The virtualenv command is failing, but because it outputs to stdout the error is being ignored (aside: it would be a good idea to check the error code here instead of just stderr). Then conftest tries to continue without a virtualenv, leading to the error pasted above.

Environment:

• OS: Debian sid

[ukch]

One solution to this problem is to change the following:

diff --git a/tests/conftest.py b/tests/conftest.py
index f585016..5d2356c 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -39,7 +39,7 @@ def env_vars():
 @pytest.fixture(scope='session')
 def venv_fresh():
     with TemporaryDirectory() as folder:
-        venv_cmd = 'virtualenv --no-pip --no-wheel --no-setuptools'
+        venv_cmd = 'virtualenv --no-pip --no-wheel --no-setuptools --python=python3'
         cmd = '{} {}'.format(venv_cmd, folder)
         proc = Popen(cmd.split(' '), stderr=PIPE, stdout=PIPE)
         out, err = proc.communicate()

[gtalarico]

Thanks for digging into this.
Surprised it works on my computer and Ci.
Both have python 2 installed.

Project is py3 only so probably makes sense to explicitly select py3 on venv creation anyhow.