classes.py

from __future__ import unicode_literals



class ValueAndString(object):
    def __init__(self, value, string):
        self.value = value
        self.string = string
        if type(string) != unicode:
            raise ValueError('Error!')


    def __eq__(self, other):
        return self.value == other.value and self.string == other.string

conftest.py

from __future__ import unicode_literals
import pytest
from classes import ValueAndString


pytest_plugins = [
    b'plugin_fixture'
]

class ConftestFixture(object):
    def foo(self):
        assert ValueAndString(1, 'lkajflaskjfalskf') == ValueAndString(2, 'lkajflaskjfalskf')


@pytest.fixture
def conftest_fixture():
    return ConftestFixture()

plugin_fixture.py

from __future__ import unicode_literals
import pytest
from classes import ValueAndString


class PluginFixture(object):
    def foo(self):
        assert ValueAndString(2, 'lkajflaskjfalskf') == ValueAndString(1, 'lkajflaskjfalskf')


@pytest.fixture
def plugin_fixture():
    return PluginFixture()

run_pyframe_eval.py

from __future__ import unicode_literals
import sys
from py._code.code import Frame


def foo():
    previous_frame = Frame(sys._getframe(-1))
    foo_string = previous_frame.eval("'foo'")
    print type(foo_string)  # should be 'unicode', but it is 'str'


def main():
    foo()

if __name__ == '__main__':
    main()

test_unicode_error_with_plugin_fixture.py

from __future__ import unicode_literals
import pytest
from classes import ValueAndString



class InlineFixture(object):
    def foo(self):
        assert ValueAndString(2, 'lkajflaskjfalskf') == ValueAndString(1, 'lkajflaskjfalskf')


@pytest.fixture
def inline_fixture():
    return InlineFixture()


def test_plugin_fixture(plugin_fixture):
    with pytest.raises(AssertionError) as e:
        plugin_fixture.foo()

    msg = e.value.msg
    assert msg.startswith('assert <classes.ValueAndString object'), msg


def test_conftest_fixture(conftest_fixture):
    with pytest.raises(AssertionError) as e:
        conftest_fixture.foo()
    msg = e.value.msg
    assert msg.startswith('assert <classes.ValueAndString object'), msg


def test_inline_fixture(inline_fixture):
    with pytest.raises(AssertionError) as e:
        inline_fixture.foo()
    msg = e.value.msg
    assert msg.startswith('assert <classes.ValueAndString object'), msg


def test_no_fixture():
    with pytest.raises(AssertionError) as e:
        assert ValueAndString(1, 'lkajflaskjfalskf') == ValueAndString(2, 'lkajflaskjfalskf')
    msg = e.value.msg
    assert msg.startswith('assert <classes.ValueAndString object'), msg