Just ask about either Amendment.
If what you get back is a spirited defense of the ideas of this country's Founding Fathers, what you've got is a libertarian. By shameful default, libertarians have become America's last and only reliable stewards of the Bill of Rights.
But if -- and this usually seems a bit more difficult to most people -- you'd like to know whether an individual is a libertarian or a conservative, ask about Abraham Lincoln.
Suppose a woman -- with plenty of personal faults herself, let that be stipulated -- desired to leave her husband: partly because he made a regular practice, in order to go out and get drunk, of stealing money she had earned herself by raising chickens or taking in laundry; and partly because he'd already demonstrated a proclivity for domestic violence the first time she'd complained about his stealing.
Now, when he stood in the doorway and beat her to a bloody pulp to keep her home, would we memorialize him as a hero? Or would we treat him like a dangerous lunatic who should be locked up, if for no other reason, then for trying to maintain the appearance of a relationship where there wasn't a relationship any more? What value, we would ask, does he find in continuing to possess her in an involuntary association, when her heart and mind had left him long ago?
History tells us that Lincoln was a politically ambitious lawyer who eagerly prostituted himself to northern industrialists who were unwilling to pay world prices for their raw materials and who, rather than practice real capitalism, enlisted brute government force -- "sell to us at our price or pay a fine that'll put you out of business" -- for dealing with uncooperative southern suppliers. That's what a tariff's all about. In support of this "noble principle", when southerners demonstrated what amounted to no more than token resistance, Lincoln permitted an internal war to begin that butchered more Americans than all of this country's foreign wars -- before or afterward -- rolled into one.
Lincoln saw the introduction of total war on the American continent -- indiscriminate mass slaughter and destruction without regard to age, gender, or combat status of the victims -- and oversaw the systematic shelling and burning of entire cities for strategic and tactical purposes. For the same purposes, Lincoln declared, rather late in the war, that black slaves were now free in the south -- where he had no effective jurisdiction -- while declaring at the same time, somewhat more quietly but for the record nonetheless, that if maintaining slavery could have won his war for him, he'd have done that, instead.