“We're going to need to run some tests, just to make sure.”
You went to the doctor because of a strange bump on your wrist. Your doctor thinks it's something harmless, but wants to make sure that it's not cancer or something else bad. He says this.
We're going to need to run some tests, just to make sure.
To "make sure" means to check something again, so that you know that it's OK. When you want something to happen and it's important, you check to "make sure" that it happens. For example, before your house guests leave, you can tell them:
Make sure you've got everything.
Or when someone is grilling some meat:
A more formal version of this phrase is "make sure that (clause)":
Make sure that the pork chops are cooked all the way through.
In a corporate office job, people are very careful not to make any mistakes, so they often talk about "making sure" of things.
When you need to do something that's going to upset your listener, you can tell them this way:
I'm going to need to ask you to leave.
We're going to need to hold back on paying bonuses this quarter.
This basically means "I have to do this, although I don't want to.
Another similar phrase is "going to have to":
But "going to have to" seems less negative.
"Running some tests" means doing tests to look for different medical problems. For example, when a cardiologist (heart doctor) "runs some tests", he or she might hook you up to a heart monitor, measure your cholestorol, measure the amount of cholesterol in your blood, and so on.
It's also possible to "run some tests" on a computer system.