Will reading it make people say, "Oh, a Star Wars rip-off", or "Harry Potter rip-off"?
I don't think there is a test you can learn and apply, and plots are recycled all the time. There is a whole industry of teaching people to write to what is basically the same plot, again and again and again.
The problem with clichés is people are bored because they have been done before, and they want something new and imaginative.
So if you write very close to the exact plot of something very popular, you have a similar problem, with gaining popularity, or sales, or even getting it published in the first place.
For example, in Dead Like Me, Liv is a zombie and eats brains; but as long as she remains fed she can pass for a regular human with regular emotions, including love, and so on.
So nobody reads that story and says, "Oh, another Walking Dead." It is nothing like that. But if you stumbled across much the same idea as Dead Like Me, people hoping for something new might say "Oh, a Dead Like Me rip-off."
This especially applies to literary agents, studio script-readers, and other gatekeepers that get books published, TV series made, or movies made. They know a lot of material within their favorite genres, and though there often is some commonality in plot structure (Romances basically have the same plot again and again), they are still looking for what feels like new and original takes on that basic setup.
So I'd say the only test is a straightforward but time-consuming one; you have to look for bestsellers (or the equivalent in movies or TV series) in the same genre as your own, and through synopsis or book jacket blurbs or plot summaries or whatever, see if any of those are strongly reminiscent of your own work. Try to be unbiased, what counts is not the details but the broad strokes of situation, main characters and setting that stick in reader's minds. So it won't make a difference if your wood elf is on a quest to destroy an evil amulet, recruited by an old forest wizard named Mar'a'Jekley, etc. If the synopsis of your plot makes people think you ripped off the plot of Lord of The Rings, you're toast, whether you actually intended to do that or did not.
With the Internet it is straightforward to find the best sellers you will be grouped with and the top sellers in that genre (say 20 or so, but use your judgment in the cut-off). But it can be a tedious afternoon, trying to find a jacket-blurb or synopsis on all of them. If you can't find those with Google in 15 minutes of search or so, you probably don't have to worry about it. Google the title and perhaps the author's name. If you can't get worthwhile hits on those, you probably don't need to worry about that one (because even if your story IS much like it, it isn't popular or current enough to pop into reader's minds as "done already").
Knowing you don't look like a rip-off of any blockbuster title is hopefully enough to give you confidence you have done something original, or original enough.