Python3 + pytest + pytest-mock: Mocks leaking into other test functions breaking assertions?

Hi guys! First of all, thank you for everything that you do! It is really appreciated!

My Question

Apologies in advance if this issue is blatant, but i’ve been wrestling with it for several days now. Hopefully someone can shed some new light.

I’m in the process of converting unit tests for my personal project from unittest -> pytest. Previously I was using the built-in unittest.mock module, but now i’m trying to use the pytest-mock plugin instead.

I have a sneaking feeling that my tests are leaking mock objects into one another.

Here’s why: NOTE: All Details about my setup (python version, modules etc) listed at bottom of question.

High-level details:

# Python version
Python 3.5.2

# Pytest version ( and plugins )
pytest==3.0.7
pytest-benchmark==3.1.0a2
pytest-catchlog==1.2.2
pytest-cov==2.4.0
pytest-ipdb==0.1.dev2
pytest-leaks==0.2.2
pytest-mock==1.6.0
pytest-rerunfailures==2.1.0
pytest-sugar==0.8.0
pytest-timeout==1.2.0
python-dateutil==2.6.0
python-dbusmock==0.16.7

When I run my tests using the following command:

py.test --pdb --showlocals -v -R : -k test_subprocess.py

Everything is fine till we get to test_subprocess_check_command_type. At which point I get the following error:

            # Set mock return types
            # mock_map_type_to_command.return_value = int
    
            # action
            with pytest.raises(TypeError) as excinfo:
                scarlett_os.subprocess.Subprocess(test_command,
                                                  name=test_name,
                                                  fork=test_fork,
    >                                             run_check_command=True)
    E           Failed: DID NOT RAISE <class 'TypeError'>
    
    excinfo    = <[AttributeError("'ExceptionInfo' object has no attribute 'typename'") raised in repr()] ExceptionInfo object at 0x7f8c380f9dc0>
    mock_fork  = <Mock name='mock_fork' id='140240122195184'>
    mock_logging_debug = <Mock name='mock_logging_debug' id='140240128747640'>
    mock_map_type_to_command = <Mock name='mock_map_type_to_command' id='140240122785112'>
    mocker     = <pytest_mock.MockFixture object at 0x7f8c329f07a8>
    monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x7f8c329f0810>
    self       = <tests.test_subprocess.TestScarlettSubprocess object at 0x7f8c32aaac20>
    test_command = ['who', '-b']
    test_fork  = False
    test_name  = 'test_who'
    
    tests/test_subprocess.py:267: Failed
    
     tests/test_subprocess.py::TestScarlettSubprocess.test_subprocess_check_command_type ⨯                                                           100% ██████████

BUT!

If I filter out all of the other tests except for the problematic one then I get:

via py.test --pdb --showlocals -v -R : -k test_subprocess_check_command_type

    pi@0728af726f1f:~/dev/bossjones-github/scarlett_os$ py.test --pdb --showlocals -v -R : -k test_subprocess_check_command_type
    /usr/local/lib/python3.5/site-packages/_pdbpp_path_hack/pdb.py:4: ResourceWarning: unclosed file <_io.TextIOWrapper name='/usr/local/lib/python3.5/site-packages/pdb.py' mode='r' encoding='UTF-8'>
      os.path.dirname(os.path.dirname(__file__)), 'pdb.py')).read(), os.path.join(
    Test session starts (platform: linux, Python 3.5.2, pytest 3.0.7, pytest-sugar 0.8.0)
    cachedir: .cache
    benchmark: 3.1.0a2 (defaults: timer=time.perf_counter disable_gc=False min_rounds=5 min_time=0.000005 max_time=1.0 calibration_precision=10 warmup=False warmup_iterations=100000)
    rootdir: /home/pi/dev/bossjones-github/scarlett_os, inifile: setup.cfg
    plugins: timeout-1.2.0, sugar-0.8.0, rerunfailures-2.1.0, mock-1.6.0, leaks-0.2.2, ipdb-0.1.dev2, cov-2.4.0, catchlog-1.2.2, benchmark-3.1.0a2
    timeout: 60.0s method: signal
    NOTE: DBUS_SESSION_BUS_ADDRESS environment var not found!
    [DBUS_SESSION_BUS_ADDRESS]: unix:path=/tmp/dbus_proxy_outside_socket
    
     tests/test_subprocess.py::TestScarlettSubprocess.test_subprocess_check_command_type ✓                                                                                                                                                                           100% ██████████
    
    Results (8.39s):
           1 passed
         190 deselected
    pi@0728af726f1f:~/dev/bossjones-github/scarlett_os$

I also tried manually commenting out the following 2 tests and they allowed me to successfully run all the tests again:

• test_subprocess_init
• test_subprocess_map_type_to_command

Can anyone see anything blatently wrong with my setup? I’ve read several blog posts on “where to mock”, and looked at the docs themselves several times, not sure what i’m missing. https://docs.python.org/3/library/unittest.mock.html

My Setup Details

Here is everything that might be required to solve this. Let me know if I need to provide any more information!

Also … please excuse how messy my code looks and all of the comment blocks. I’m a big note taker when i’m learning something new … I’ll make everything more pythonic and cleaner in the near future 😃

My code:

    #!/usr/bin/env python
    # -*- coding: utf-8 -*-

    """Scarlett Dbus Service. Implemented via MPRIS D-Bus Interface Specification."""

    from __future__ import with_statement, division, absolute_import

    import os
    import sys
    from scarlett_os.exceptions import SubProcessError
    from scarlett_os.exceptions import TimeOutError
    import logging
    from scarlett_os.internal.gi import GObject
    from scarlett_os.internal.gi import GLib

    logger = logging.getLogger(__name__)


    def check_pid(pid):
        """Check For the existence of a unix pid."""
        try:
            os.kill(pid, 0)
        except OSError:
            return False
        else:
            return True


    class Subprocess(GObject.GObject):
        """
        GObject API for handling child processes.

        :param command: The command to be run as a subprocess.
        :param fork: If `True` this process will be detached from its parent and
                     run independent. This means that no excited-signal will be emited.

        :type command: `list`
        :type fork: `bool`
        """

        __gtype_name__ = 'Subprocess'
        __gsignals__ = {
            'exited': (GObject.SignalFlags.RUN_LAST, None, (GObject.TYPE_INT, GObject.TYPE_INT))
        }

        def __init__(self, command, name=None, fork=False, run_check_command=True):
            """Create instance of Subprocess."""

            GObject.GObject.__init__(self)

            self.process = None
            self.pid = None

            if not fork:
                self.stdout = True
                self.stderr = True
            else:
                self.stdout = False
                self.stderr = False

            self.forked = fork

            # Verify that command is properly formatted 
            # and each argument is of type str
            if run_check_command:
                self.check_command_type(command)

            self.command = command
            self.name = name

            logger.debug("command: {}".format(self.command))
            logger.debug("name: {}".format(self.name))
            logger.debug("forked: {}".format(self.forked))
            logger.debug("process: {}".format(self.process))
            logger.debug("pid: {}".format(self.pid))

            if fork:
                self.fork()

        # TODO: Add these arguments so we can toggle stdout
        # def spawn_command(self, standard_input=False, standard_output=False, standard_error=False):
        def spawn_command(self):
            # DO_NOT_REAP_CHILD
            # Don't reap process automatically so it is possible to detect when it is closed.
            return GLib.spawn_async(self.command,
                                    flags=GLib.SpawnFlags.SEARCH_PATH | GLib.SpawnFlags.DO_NOT_REAP_CHILD
                                    )

        def map_type_to_command(self, command):
            """Return: Map after applying type to several objects in an array"""
            # NOTE: In python3, many processes that iterate over iterables return iterators themselves. 
            # In most cases, this ends up saving memory, and should make things go faster.
            # cause of that, we need to call list() over the map object
            return list(map(type, command))

        def check_command_type(self, command):

            types = self.map_type_to_command(command)

            if type(types) is not list:
                raise TypeError("Variable types should return a list in python3. Got: {}".format(types))

            # NOTE: str is a built-in function (actually a class) which converts its argument to a string. 
            # string is a module which provides common string operations.
            # source: http://stackoverflow.com/questions/2026038/relationship-between-string-module-and-str
            for t in types:
                if t is not str:
                    raise TypeError("Executables and arguments must be str objects. types: {}".format(t))

            logger.debug("Running Command: %r" % " ".join(command))
            return True

        def run(self):
            """Run the process."""

            # NOTE: DO_NOT_REAP_CHILD: the child will not be automatically reaped;
            # you must use g_child_watch_add yourself (or call waitpid or handle `SIGCHLD` yourself),
            # or the child will become a zombie.
            # source:
            # http://valadoc.org/#!api=glib-2.0/GLib.SpawnFlags.DO_NOT_REAP_CHILD

            # NOTE: SEARCH_PATH: argv[0] need not be an absolute path, it will be looked for in the user's PATH
            # source:
            # http://lazka.github.io/pgi-docs/#GLib-2.0/flags.html#GLib.SpawnFlags.SEARCH_PATH

            self.pid, self.stdin, self.stdout, self.stderr = self.spawn_command()

            logger.debug("command: {}".format(self.command))
            logger.debug("stdin: {}".format(self.stdin))
            logger.debug("stdout: {}".format(self.stdout))
            logger.debug("stderr: {}".format(self.stderr))
            logger.debug("pid: {}".format(self.pid))

            # close file descriptor
            self.pid.close()

            print(self.stderr)

            # NOTE: GLib.PRIORITY_HIGH = -100
            # Use this for high priority event sources.
            # It is not used within GLib or GTK+.
            watch = GLib.child_watch_add(GLib.PRIORITY_HIGH, 
                                         self.pid, 
                                         self.exited_cb)

            return self.pid

        def exited_cb(self, pid, condition):
            if not self.forked:
                self.emit('exited', pid, condition)

        def fork(self):
            """Fork the process."""
            try:
                # first fork
                pid = os.fork()
                if pid > 0:
                    logger.debug('pid greater than 0 first time')
                    sys.exit(0)
            except OSError as e:
                logger.error('Error forking process first time')
                sys.exit(1)

            # Change the current working directory to path.
            os.chdir("/")

            # Description: setsid() creates a new session if the calling process is not a process group leader. 
            # The calling process is the leader of the new session, 
            # the process group leader of the new process group, 
            # and has no controlling terminal. 
            # The process group ID and session ID of the calling process are set to the PID of the calling process. 
            # The calling process will be the only process in this new process group and in this new session.

            # Return Value: On success, the (new) session ID of the calling process is returned. 
            # On error, (pid_t) -1 is returned, and errno is set to indicate the error.
            os.setsid()

            # Set the current numeric umask and return the previous umask.
            os.umask(0)

            try:
                # second fork
                pid = os.fork()
                if pid > 0:
                    logger.debug('pid greater than 0 second time')
                    sys.exit(0)
            except OSError as e:
                logger.error('Error forking process second time')
                sys.exit(1)

My Test:

    #!/usr/bin/env python
    # -*- coding: utf-8 -*-

    """
    test_subprocess
    ----------------------------------
    """

    import os
    import sys
    import pytest

    import scarlett_os
    # import signal
    # import builtins
    # import re

    class TestScarlettSubprocess(object):
        '''Units tests for Scarlett Subprocess, subclass of GObject.Gobject.'''

        def test_check_pid_os_error(self, mocker):
            # Feels like mocks are leaking into other tests, 
            # stop mock before starting each test function
            mocker.stopall()

            # Setup mock objects
            kill_mock = mocker.MagicMock(name=__name__ + "_kill_mock_OSError")
            kill_mock.side_effect = OSError

            # patch things
            mocker.patch.object(scarlett_os.subprocess.os, 'kill', kill_mock)

            # When OSError occurs, throw False
            assert not scarlett_os.subprocess.check_pid(4353634632623)
            # Verify that os.kill only called once
            assert kill_mock.call_count == 1

        def test_check_pid(self, mocker):
            # Feels like mocks are leaking into other tests, 
            # stop mock before starting each test function
            mocker.stopall()

            # Setup mock objects
            kill_mock = mocker.MagicMock(name=__name__ + "_kill_mock")

            mocker.patch.object(scarlett_os.subprocess.os, 'kill', kill_mock)

            result = scarlett_os.subprocess.check_pid(123)
            assert kill_mock.called
            # NOTE: test against signal 0
            # sending the signal 0 to a given PID just checks if any
            # process with the given PID is running and you have the
            # permission to send a signal to it.
            kill_mock.assert_called_once_with(123, 0)
            assert result is True

        # FIXME: I THINK THIS GUYS IS LEAKING MOCK OBJECTS
        def test_subprocess_init(self, mocker):
            # Feels like mocks are leaking into other tests, 
            # stop mock before starting each test function
            mocker.stopall()

            mock_check_command_type = MagicMock(name="mock_check_command_type")
            mock_check_command_type.return_value = True
            mock_fork = mocker.MagicMock(name="mock_fork")
            mock_logging_debug = mocker.MagicMock(name="mock_logging_debug")

            # mock
            mocker.patch.object(scarlett_os.subprocess.logging.Logger, 'debug', mock_logging_debug)
            mocker.patch.object(scarlett_os.subprocess.Subprocess, 'check_command_type', mock_check_command_type)
            mocker.patch.object(scarlett_os.subprocess.Subprocess, 'fork', mock_fork)

            # NOTE: On purpose this is an invalid cmd. Should be of type array
            test_command = ['who']

            test_name = 'test_who'
            test_fork = False

            s_test = scarlett_os.subprocess.Subprocess(test_command,
                                                       name=test_name,
                                                       fork=test_fork)

            # action
            assert s_test.check_command_type(test_command) is True
            mock_check_command_type.assert_called_with(['who'])
            assert not s_test.process
            assert not s_test.pid
            assert s_test.name == 'test_who'
            assert not s_test.forked
            assert s_test.stdout is True
            assert s_test.stderr is True

            mock_logging_debug.assert_any_call("command: ['who']")
            mock_logging_debug.assert_any_call("name: test_who")
            mock_logging_debug.assert_any_call("forked: False")
            mock_logging_debug.assert_any_call("process: None")
            mock_logging_debug.assert_any_call("pid: None")
            mock_fork.assert_not_called()

        # FIXME: I THINK THIS GUYS IS LEAKING MOCK OBJECTS
        def test_subprocess_map_type_to_command(self, mocker):
            """Using the mock.patch decorator (removes the need to import builtins)"""
            # Feels like mocks are leaking into other tests, 
            # stop mock before starting each test function
            mocker.stopall()

            mock_check_command_type = mocker.MagicMock(name="mock_check_command_type")
            mock_check_command_type.return_value = True
            mock_fork = mocker.MagicMock(name="mock_fork")
            mock_logging_debug = mocker.MagicMock(name="mock_logging_debug")

            # mock
            mocker.patch.object(scarlett_os.subprocess.logging.Logger, 'debug', mock_logging_debug)
            mocker.patch.object(scarlett_os.subprocess.Subprocess, 'check_command_type', mock_check_command_type)
            mocker.patch.object(scarlett_os.subprocess.Subprocess, 'fork', mock_fork)

            # NOTE: On purpose this is an invalid cmd. Should be of type array
            test_command = ["who", "-b"]
            test_name = 'test_who'
            test_fork = False

            # create subprocess object
            s_test = scarlett_os.subprocess.Subprocess(test_command,
                                                       name=test_name,
                                                       fork=test_fork)
            mocker.spy(s_test, 'map_type_to_command')
            assert isinstance(s_test.map_type_to_command(test_command), list)
            assert s_test.map_type_to_command.call_count == 1

            assert s_test.check_command_type(test_command)
            assert s_test.check_command_type(
                test_command) == mock_check_command_type.return_value

        def test_subprocess_check_command_type(self, mocker):
            """Using the mock.patch decorator (removes the need to import builtins)"""
            # Feels like mocks are leaking into other tests, 
            # stop mock before starting each test function
            mocker.stopall()

            test_command = ["who", "-b"]
            test_name = 'test_who'
            test_fork = False

            # mock
            mock_map_type_to_command = mocker.MagicMock(name="mock_map_type_to_command")
            # mock_map_type_to_command.return_value = int
            mock_map_type_to_command.side_effect = [int, [int, int]]
            mock_fork = mocker.MagicMock(name="mock_fork")
            mock_logging_debug = mocker.MagicMock(name="mock_logging_debug")

            mocker.patch.object(scarlett_os.subprocess.logging.Logger, 'debug', mock_logging_debug)
            mocker.patch.object(scarlett_os.subprocess.Subprocess, 'map_type_to_command', mock_map_type_to_command)
            mocker.patch.object(scarlett_os.subprocess.Subprocess, 'fork', mock_fork)


            # action
            with pytest.raises(TypeError) as excinfo:
                scarlett_os.subprocess.Subprocess(test_command,
                                                  name=test_name,
                                                  fork=test_fork,
                                                  run_check_command=True)
            assert str(
                excinfo.value) == "Variable types should return a list in python3. Got: <class 'int'>"

            with pytest.raises(TypeError) as excinfo:
                scarlett_os.subprocess.Subprocess(test_command,
                                                  name=test_name,
                                                  fork=test_fork,
                                                  run_check_command=True)

            assert str(
                excinfo.value) == "Executables and arguments must be str objects. types: <class 'int'>"

My folder structure( Note I removed a couple things since it was overly verbose ):

    pi@0728af726f1f:~/dev/bossjones-github/scarlett_os$ tree -I *.pyc
    .
    ├── requirements_dev.txt
    ├── requirements_test_experimental.txt
    ├── requirements_test.txt
    ├── requirements.txt
    ├── scarlett_os
    │   ├── automations
    │   │   ├── __init__.py
    │   │   └── __pycache__
    │   ├── commands.py
    │   ├── compat.py
    │   ├── config.py
    │   ├── const.py
    │   ├── core.py
    │   ├── emitter.py
    │   ├── exceptions.py
    │   ├── __init__.py
    │   ├── internal
    │   │   ├── debugger.py
    │   │   ├── deps.py
    │   │   ├── encoding.py
    │   │   ├── formatting.py
    │   │   ├── gi.py
    │   │   ├── __init__.py
    │   │   ├── path.py
    │   │   ├── __pycache__
    │   │   └── system_utils.py
    │   ├── listener.py
    │   ├── loader.py
    │   ├── logger.py
    │   ├── log.py
    │   ├── __main__.py
    │   ├── mpris.py
    │   ├── player.py
    │   ├── __pycache__
    │   ├── receiver.py
    │   ├── speaker.py
    │   ├── subprocess.py
    │   ├── tasker.py
    │   ├── tools
    │   │   ├── __init__.py
    │   │   ├── package.py
    │   │   ├── __pycache__
    │   │   └── verify.py
    │   └── utility
    │       ├── audio.py
    │       ├── dbus_runner.py
    │       ├── dbus_utils.py
    │       ├── distance.py
    │       ├── dt.py
    │       ├── file.py
    │       ├── generators.py
    │       ├── gnome.py
    │       ├── __init__.py
    │       ├── location.py
    │       ├── __pycache__
    │       ├── temperature.py
    │       ├── threadmanager.py
    │       ├── thread.py
    │       ├── unit_system.py
    │       └── yaml.py
    ├── setup.cfg
    ├── setup.py
    ├── tests
    │   ├── common_integration.py
    │   ├── common.py
    │   ├── helpers
    │   │   ├── __init__.py
    │   │   ├── __pycache__
    │   │   ├── test_config_validation.py
    │   │   ├── test_entity.py
    │   │   └── test_init.py
    │   ├── __init__.py
    │   ├── integration
    │   │   ├── baseclass.py
    │   │   ├── conftest.py
    │   │   ├── __init__.py
    │   │   ├── __pycache__
    │   │   ├── README.md
    │   │   ├── stubs.py
    │   │   ├── test_integration_end_to_end.py
    │   │   ├── test_integration_listener.py
    │   │   ├── test_integration_mpris.py
    │   │   ├── test_integration_player.py
    │   │   ├── test_integration_tasker.py
    │   │   ├── test_integration_tasker.py.enable_sound.diff
    │   │   └── test_integration_threadmanager.py
    │   ├── internal
    │   │   ├── __init__.py
    │   │   ├── __pycache__
    │   │   ├── test_deps.py
    │   │   ├── test_encoding.py
    │   │   └── test_path.py
    │   ├── performancetests
    │   │   ├── baseclass.py
    │   │   ├── __init__.py
    │   │   └── __pycache__
    │   ├── __pycache__
    │   ├── run_all_tests
    │   ├── run_dbus_tests.sh
    │   ├── test_cli.py
    │   ├── test_commands.py
    │   ├── testing_config
    │   │   └── custom_automations
    │   │       ├── light
    │   │       │   └── test.py
    │   │       └── switch
    │   │           └── test.py
    │   ├── test_listener.py
    │   ├── test_mpris.py
    │   ├── test_player.py
    │   ├── test_scarlett_os.py
    │   ├── test_speaker.py
    │   ├── test_subprocess.py
    │   ├── test_tasker.py
    │   ├── test_threadmanager.py
    │   ├── tools_common.py
    │   ├── unit_scarlett_os.py
    │   └── utility
    │       ├── __init__.py
    │       ├── __pycache__
    │       ├── test_dbus_utils.py
    │       ├── test_distance.py
    │       ├── test_dt.py
    │       ├── test_gnome.py
    │       ├── test_init.py
    │       ├── test_location.py
    │       ├── test_unit_system.py
    │       └── test_yaml.py
    67 directories, 256 files
    pi@0728af726f1f:~/dev/bossjones-github/scarlett_os$

Other details( Extended pip freeze just in case of incompatibilities ):

    # Python version
    Python 3.5.2

    # Pytest version ( and plugins )
    pytest==3.0.7
    pytest-benchmark==3.1.0a2
    pytest-catchlog==1.2.2
    pytest-cov==2.4.0
    pytest-ipdb==0.1.dev2
    pytest-leaks==0.2.2
    pytest-mock==1.6.0
    pytest-rerunfailures==2.1.0
    pytest-sugar==0.8.0
    pytest-timeout==1.2.0
    python-dateutil==2.6.0
    python-dbusmock==0.16.7


    # Pip Freeze ( Just in case )
    alabaster==0.7.10
    appdirs==1.4.3
    argh==0.26.2
    asn1crypto==0.22.0
    astroid==1.5.2
    Babel==2.4.0
    bleach==2.0.0
    bumpversion==0.5.3
    cffi==1.10.0
    click==6.7
    click-plugins==1.0.3
    colorama==0.3.7
    colorlog==2.10.0
    coverage==4.3.4
    coveralls==1.1
    cryptography==1.8.1
    Cython==0.25.2
    decorator==4.0.11
    docopt==0.6.2
    docutils==0.13.1
    ecdsa==0.13
    entrypoints==0.2.2
    Fabric3==1.12.post1
    fancycompleter==0.7
    fields==5.0.0
    flake8==3.3.0
    flake8-docstrings==1.0.3
    flake8-polyfill==1.0.1
    freezegun==0.3.8
    gnureadline==6.3.3
    graphviz==0.6
    html5lib==0.999999999
    hunter==1.4.1
    idna==2.5
    imagesize==0.7.1
    ipdb==0.10.2
    ipykernel==4.6.1
    ipython==6.0.0
    ipython-genutils==0.2.0
    ipywidgets==6.0.0
    isort==4.2.5
    jedi==0.10.2
    Jinja2==2.9.6
    jsonschema==2.6.0
    jupyter==1.0.0
    jupyter-client==5.0.1
    jupyter-console==5.1.0
    jupyter-core==4.3.0
    lazy-object-proxy==1.2.2
    MarkupSafe==1.0
    mccabe==0.6.1
    mistune==0.7.4
    mock==2.0.0
    mock-open==1.3.1
    mypy-lang==0.4.6
    nbconvert==5.1.1
    nbformat==4.3.0
    notebook==5.0.0
    objgraph==3.1.0
    ordereddict==1.1
    packaging==16.8
    pandocfilters==1.4.1
    paramiko==1.18.2
    pathtools==0.1.2
    pbr==1.10.0
    pdbpp==0.8.3
    pexpect==4.2.1
    pickleshare==0.7.4
    pluggy==0.4.0
    plumbum==1.6.3
    prompt-toolkit==1.0.14
    psutil==5.2.2
    ptyprocess==0.5.1
    py==1.4.33
    py-cpuinfo==3.2.0
    pyasn1==0.2.3
    pycodestyle==2.3.1
    pycparser==2.17
    pycrypto==2.6.1
    pydbus==0.6.0
    pydocstyle==2.0.0
    pyflakes==1.5.0
    pygal==2.3.1
    pygaljs==1.0.1
    Pygments==2.2.0
    pygobject==3.22.0
    pylint==1.7.1
    pyparsing==2.2.0
    pystuck==0.8.5
    pytest==3.0.7
    pytest-benchmark==3.1.0a2
    pytest-catchlog==1.2.2
    pytest-cov==2.4.0
    pytest-ipdb==0.1.dev2
    pytest-leaks==0.2.2
    pytest-mock==1.6.0
    pytest-rerunfailures==2.1.0
    pytest-sugar==0.8.0
    pytest-timeout==1.2.0
    python-dateutil==2.6.0
    python-dbusmock==0.16.7
    pytz==2017.2
    PyYAML==3.12
    pyzmq==16.0.2
    qtconsole==4.3.0
    requests==2.13.0
    requests-mock==1.3.0
    rpyc==3.3.0
    -e [e-mail]:bossjones/scarlett_os.git@c14ffcde608da12f5c2d4d9b81a63c7e618b3eed#egg=scarlett_os
    simplegeneric==0.8.1
    six==1.10.0
    snowballstemmer==1.2.1
    Sphinx==1.5.5
    stevedore==1.18.0
    termcolor==1.1.0
    terminado==0.6
    testpath==0.3
    tornado==4.5.1
    tox==2.7.0
    traitlets==4.3.2
    typing==3.6.1
    virtualenv==15.0.3
    virtualenv-clone==0.2.6
    virtualenvwrapper==4.7.2
    voluptuous==0.9.3
    watchdog==0.8.3
    wcwidth==0.1.7
    webencodings==0.5.1
    widgetsnbextension==2.0.0
    wmctrl==0.3
    wrapt==1.10.10
    xdot==0.7

[nicoddemus]

The problem is that you are assigning the mock object directly:

m.ClassTest.fun_test = mocker.MagicMock()

mocker can’t know that it should undo that assignment in that case. Mocking like this for instances is fine because you would be changing only that instance, but by doing in the class you are effectively doing that globally and permanently.

Use mocker.patch.object instead:

mocker.patch.object(m.ClassTest, 'fun_test')

Then your example works as expected for me:

collected 4 items

foo.py .F..

================================== FAILURES ===================================
_____________________________ TestMock.test_mock ______________________________

self = <foo.TestMock object at 0x000001D10A7C1160>
mocker = <pytest_mock.MockFixture object at 0x000001D10A7C12E8>

    def test_mock(self, mocker):
        mocker.patch.object(ClassTest, 'fun_test')
        c = ClassTest()
        c.fun_test()
        print(c.fun_test())  # This is a mock
>       assert 1==2
E       assert 1 == 2

foo.py:16: AssertionError
---------------------------- Captured stdout call -----------------------------
<MagicMock name='fun_test()' id='1997335725616'>
===================== 1 failed, 3 passed in 0.17 seconds ======================

[dimaqq]

Exception text seems very similar to http://programtalk.com/python-examples/qibuild.build.BuildFailed/ example 2 “test_qibuild_make.py”. Perhaps there is a bug?