This is actually supported natively in py.test via indirect parametrization.
In your case, you would have:
@pytest.fixture
def tester(request):
"""Create tester object"""
return MyTester(request.param)
class TestIt:
@pytest.mark.parametrize('tester', [['var1', 'var2']], indirect=True)
def test_tc1(self, tester):
tester.dothis()
assert 1