A litmus test isn't just a policy position. In a different post, you said you wouldn't vote for anybody who didn't support repeal of Citizen's United ruling. It is a policy position but one you use to screen candidates much like one tests pH of an aqueous solution using litmus paper.
I have a few strongly held positions. Unsurprisingly not bottom line issues. Such as a woman's right to choose. It would be a dark day if I ever saw a candidate holding anti-choice position as the best one. Anybody who talks incessantly about race and sex in the way Trump does would be off my list. Knowing what we know now, a wealthy man would have to agree to putting his entire holdings into a trust in a manner that would avoid the appearance of ethics issues.
There was nothing about either Clinton or Sanders would have made them unacceptable to me.
This is nuanced, however. Just because I say racist actions or omissions regarding race in speeches wouldn't be a litmus test, doesn't mean it wouldn't affect my vote. I'm not much impressed with dumbshit yes-no criteria because it dumbs down the discussion. Clinton most certainly supported her husband's bill that ended up incarcerating millions more African Americans and said some startlingly ignorant things too. And so, of course I think she is affected by race-bias at the very least. Yet, she has the endorsement of major African American groups compared to the one black man who liked Bernie. (overstated to make a point, calm down).
I went to Justice Democrats home page and went through their list.
JD policies that can be litmus test policies to me:
Protect Medicare, Medicaid, Social Security
Defend and Protect Women's rights
https://justicedemocrats.com/Platform
There are a lot of issues that I expect my candidate to support listed there but I'm more interested in hearing what the candidate says rather than put a box next to that line item to check off for compliance.
Missing on that list is equal pay for equal work. If a candidate doesn't have something like that in their postion/policy statement, I'm going to look hard at other candidates. Also missing on that list is Defend the rights of minorities. That would include black, brown, LGBTQ, retired ex-pat Canadian hockey players.
I'll never not vote, even if my choice of candidates doesn't meet my low bar in terms of a litmus test. Too many gave their lives for that right and I won't disrespect them.