Yes, JIRA doesn't have a "tests" thing built into it, so you will need an add-on.
However, there are a lot of options for a testing add-on. Testrail, Test Management for JIRA, Zephyr (Server or inside JIRA), qTest, and and and.
You'll need to define what you want from a testing add-on and have a look at all the options in the marketplace.
I'm not aware of any specifically open-source ones. I look at the features my clients need and then cost.
If cost is the primary thing you need to worry about, then that's fine, but I'm afraid I can't really suggest or recommend any product. You need to decide on what you're looking for and then have a look through https://marketplace.atlassian.com/solutions/test-management-tools-for-jira
In the interests of openness, I work for one of the providers listed there (albeit not in that area). That does not change my recommendation that you should evaluate your options against what you need and want.
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