I'm not going to pretend to have the answers. I don't know what makes someone a good parent. It's my serious suspicion that there are no good parents, only bad parents, and the ones we call "good" are just the least bad ones. There are certain qualities one attributes to being either a "good" parent, or a bad one. Being a bad parent is pretty cut and dry. Being emotionally or physically neglectful or abusive will generally constitute bad parenting. Letting your kid eat candy for breakfast every day. Not policing their behavior when they act up. Instilling bad habits and ethics by indoctrination. But as you filter down from the truly terrible stuff, it's hard to know what exactly makes a "good" or at least "not bad" parent.
For instance, some might argue that allowing a small child to play football, where they might, say, sustain a head injury, is poor parenting. Others might say emotional over-sharing is detrimental. I mean, some people think vaccinating children is irresponsible parenting. (I think those people are wrong, but whatever.) The point is, where there's no tangible adversity for a child, it's tough to call someone a bad parent, because even though I don't have kids yet, one thing I know for sure is that parenting is HARD. Seeing qualities in your SO that will easy the difficulty of child rearing is probably a good sign that they're going to be a parent that falls into the happy face side of the scale. So here are some signs that your SO might actually make a pretty great parent:
1. They're patient
Do you know how dumb kids are? "Pretty" to "very". Meanwhile, think about all the school recitals you're going to have to sit through. A good parent is a patient parent.
2. They're not easily grossed out
Ask anyone you know who is a parent if they've ever gotten their child's poop on their face. I bet 100% will say "yes" and 80% will say, "...and a little in my mouth." I've worked as a babysitter in the past and even I've been pooped, peed, and vomited all over. Kids are basically just walking, uncontrollable defecating machines. If your SO is someone who can stomach the unsightly, they might be more primed for parenting than most.
3. They love unconditionally
If your SO is only "in" when things are good, they're probably not going to be the best person to have around when your kid is wailing at 3AM because they have an ear ache. Kids, from what I know of them, can be the worst. And you have to love them when they're terrible as much as you love them when they're adorable.
4. They're able to "put their foot down"
There's something really sexy about having an SO who can call you out and be firm with you when you're being ridiculous, without ever being mean or condescending or yelling. That sexiness is your uterus falling to the floor because you know this is the kind of person that will destroy a naughty child with lines like, "I'm not mad, I'm just disappointed". SHUDDER.
5. They have a generally positive attitude to life
You don't want a parent around who is constantly negative about everything. You know who's a negative nancy? Every teenager ever. It's a parent's job to present positivity, so having an SO who can see the silver lining is a nice little portent for your future family.
6. They're creative
Finding new ways to entertain children isn't that hard, but there's only so long you can occupy them with sticking macaroni and glitter to things. A creative spirit is a useful tool for parents.
7. They embrace change
I hear every day is different and brings new challenges when you're a parent, so an SO who can roll with the punches is probably going to be pretty great when you throw them in the ring.
8. They're reliable and loyal
A partner who not only does what they say they'll do, but who you trust to do what they say they'll do, is going to be a great parent. When there's a child involved, going back on promises and forgetting responsibilities wont fly the same way it might when it's just the two of you.
9. They have solid priorities
You wouldn't say a good parent is someone who prioritizes going out boozing all night and sleeping all day the next day, would you? If your partner has solid priorities that center on their responsibilities, then you're looking at a good parent. If you're looking at a constant hangover, you might not be. But then, people do adjust to accommodate children.
10. They're interested in children
I mean, if someone hates children and wants nothing to do with them then... I don't know if that's going to translate well.
11. They're willing to compromise
Life is like a box of compromises. You never know what you're going to get, and then just as you bite into the mint flavor you love the most, your stupid kid decides that's the one they want. Sigh.