Pytest calling different python interpreter (due to border effects)

I need to test some code which has border effects so my tests need to have different Python interpreter.

Is there a way to tell pytest to use a new Python instance of the python interpreter for a given Test Case.

For example, I have a class C1 that sets an environment which is needed before instantiating another class C2 (I know, not a proper implementation :) ). I need to test: * Class C1 is instantiated, then C2 is instantiated => OK * Class C2 is instantiated => Raise exception

The following code would not be proper because of the border effect

def test_OK():
    C1()
    C2()

def test_NOK():
    with pytest.raises(Exception):
        C2()

I used a workaround by creating external files run with subprocess but it is ugly like hell.

from pathlib import Path
import subprocess
import pytest

test_dir = Path(__file__).parent.absolute()
python_lib = test_dir.parent / "PythonLib"


no_standard = """
from a661test import TestFramework
from a661libgen_rev6_v1 import Label
framework = TestFramework()
framework.create_df([Label(1).define()])
"""

with_standard = """
from a661test import TestFramework
from a661libgen_rev6_v1 import Label, Standard_rev6_v1
Standard_rev6_v1()
framework = TestFramework()
framework.create_df([Label(1).define()])
"""

class Test_Framework_Nominal:
    def tc_A661_TESTFRAMEWORK_FRAMEWORK_TC_R_01(self, monkeypatch):
        """Checking an exception is raised when Standard not set"""
        monkeypatch.setenv("PYTHONPATH", str(python_lib))
        script = Path("script.py")
        script.write_text(no_standard)
        with pytest.raises(Exception):
            subprocess.run(["python", str(script)], check=True)

    def tc_A661_TESTFRAMEWORK_FRAMEWORK_TC_N_02(self, monkeypatch):
        """Checking no exception is raised if Standard is set"""
        monkeypatch.setenv("PYTHONPATH", str(python_lib))
        script = Path("script.py")
        script.write_text(with_standard)
        subprocess.run(["python", str(script)], check=True)

Is there some magic option, or plugin / setting of conftest.py that would allow something like:

@pytest.mark.new_python_instance
def test_OK():
    C1()
    C2()

@pytest.mark.new_python_instance
def test_NOK():
    with pytest.raises(Exception):
        C2()

Thanks