tox: Check that a particular environment is not supported

I have a library that is only compatible with Python 3.x. I specify that in my setup.py's setup function:

setup(
    name=PROJECT,
    version=version,
    packages=get_packages(PROJECT),
    package_data=get_package_data(PROJECT),
    python_requires=">= 3.5",
)

I also have TOX to run my test for different python versions. However, I want to make sure that the library cannot be installed on Python 2.x. And I want my CI to go green only if the lib fails to build on Python 2.

Can it be done using TOX? Does it make sense to check it in the first place?