I’m doing the IB Diploma in 1 year, but I also have the option to take ap tests along with the ib diploma. So I have a few questions:
Will it boost my application if colleges see I took the tests as well as the ib diploma?
Since colleges only award credit for IB HL classes, will taking AP tests give me more college credit, so I can save money in college in the future?
No
Yes, assuming you score high enough on the exams and the college gives credit for that exam.
No.
Possibly-- some AP exams align with SL classes, so in that case, it could help. It is also not uncommon for the AP threshold for credit be easier to achieve than the IB HL one. But also note that if you are pursuing credit, there are many schools which will give you sophomore standing for an IBD. How this is done varies wildly from school to school, but if this alone is the goal, choosing one of those schools and completing the IBD will be enough.
Thanks guys 
also, do you know if ap tests are similar to what I learn in ib sl subjects? Like, if I already did the ib sl test, would I have to study for the ap test of the same subject, or do they cover the same topic?
It really depends on the IB subject.
You’d probably be well served by picking up a prep book.
Do you mean AP tests in subjects where you are taking IB SL courses that partially overlap with the AP content (so that you would have to self-study a portion, but not all, of the AP content)?
My kid did a lot of this. For English, Foreign Languages, Business, Psychology, and History, it didn’t require any extra study. I don’t know but I’m guessing Chemistry and Biology might also be passable. It was not possible with Physics.
Sciences might be passable with a 3. A 4+ would be highly unlikely.
One issue that can occur is that the AP tests may only be offered on the same days as the IB exams. There is no flexibility with the IB schedule & you may not be able to fit in both. If you are trying to get the most college credit, AP is the way to go. A full IBD will prepare you better for college overall due to the amount of additional writing and learning time-management, but for the amount of work involved - you get very little college credit.
It’s been about 6 years, but the kids in DS’ SL Chem who did the AP exam got excellent scores. Not sure how they prepped but they said the IB SL exam was harder.
One thing to note… because the IB was designed for schools around the world and most have more class days than US schools do, it’s not unusual for a US school with an IB curriculum to choose to omit certain parts of the course. I am guessing that what’s omitted could influence the amount of overlap material with the AP, so really, your best bet is to ask the teachers at your school what other students there have encountered.
This depends on the school and the state. Every school in my state gives 24 college credits for IBD.
However, subject credit and advanced placement may not be so generous and will depend on the specific college.