gistfile1.txt

# content of conftest.py

import pytest

@pytest.mark.tryfirst
def pytest_pyfunc_call(pyfuncitem):
    marker = pyfuncitem.get_marker("skip_if_eval")
    if marker is not None:
        class Mapping:
            def __getitem__(self, name):
                if name not in pyfuncitem.fixturenames:
                    raise KeyError
                return pyfuncitem._request.getfuncargvalue(name)
        expr = marker.args[0]
        if eval(expr, {}, Mapping()):
            pytest.skip("skipped because of expression %r" % expr)

# content of test file

import pytest

@pytest.mark.skip_if_eval("tmpdir.basename")
def test_hello(tmpdir):
    pass