I recall being in ninth-grade science class and learning about something called a litmus test.

For some reason, this particular test, which according to Merriam-Webster is defined as "a test in which a single factor (such as an attitude, event, or fact) is decisive," stuck with me. The stick goes in the cup and then you find out something. I don't know, it was all very impactful to the 14-year-old me.

I have used the term "litmus test" to set up big moments in my life because it has always felt like the perfect way to describe whether what we are going to experience is for real.

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Why am I bringing this up now?

Because it seems like Conor McGregor vs. Donald Cerrone is the ultimate litmus test for McGregor at this stage in his career. On Jan. 18, we are going to find out just how real this McGregor comeback story is.

I've never liked the term "gatekeeper," and I think calling this fight a tune-up is disrespectful to Cerrone, so I think the perfect way to label this is as a litmus test. I can see it now. UFC 246: Litmus Test. Tell me that isn't brilliant marketing.

Look, I know many fans were underwhelmed by the matchup. They wanted to see McGregor fight a top contender such as Justin Gaethje because that is what we have come to expect from McGregor: He fights the very best, no matter what.

However, I think his choice of Cerrone -- and let's be honest, he could have chosen anyone not named Khabib Nurmagomedov or Tony Ferguson -- was a refreshing sign from Team McGregor. It was an acknowledgment, if you will, that McGregor, at least right now, isn't the same guy who beat Eddie Alvarez in November 2016 (his most recent win). No, he's now a guy who is trying to build himself back up. He's entering the pool via the shallow end, with the intention of swimming a full lap (or two) eventually, rather than diving straight into the deep end like in the past. I like this.

play 1:13 Helwani: 'This is the perfect fight for Conor McGregor' Ariel Helwani explains that Conor McGregor's fighting Donald Cerrone in January will allow McGregor to "get his mojo back," given that he hasn't won a fight since 2016.

Here's how McGregor's past four years have gone:

Dec. 12, 2015: Beat Jose Aldo for the UFC featherweight championship, then called for a challenge for the lightweight title.

March 5, 2016: Lost to Nathan Diaz (after the lightweight title fight fell apart because of an injury to champion Rafael Dos Anjos) and insisted on an immediate rematch.

Aug. 20, 2016: Beat Diaz, setting up a fight for the lightweight title.

Nov. 12, 2016: Beat Alvarez for the 155-pound belt, becoming a two-division champ, then looked to take on Floyd Mayweather in boxing.

Aug. 26, 2017: Lost to Mayweather in a match that broke records for revenue generated.

Oct. 6, 2018: Lost to Nurmagomedov in a challenge for the lightweight title.

It has been one big fight after the next. Time to take a step back.

The UFC will return Saturday, with an up-and-coming heavyweight looking to knock off an established veteran in the main event. Jairzinho Rozenstruik, who is 9-0 and opened eyes with his first-round KO win over Andrei Arlovski at UFC 244, will face the toughest challenge of his career in Alistair Overeem. "The Demolition Man" is 45-17 and has earned two straight first-round TKO wins. UFC Fight Night: Overeem vs. Rozenstruik

• Saturday, Washington, D.C.

•Early prelims: ESPN+, 5:30 p.m. ET

•Prelims: ESPN, 7 p.m. ET

•Main card: ESPN, 9 p.m. ET Subscribe to ESPN+ to get exclusive live UFC events, weigh-ins and more; Ariel and the Bad Guy; Dana White's Contender Series; and more exclusive MMA content.

I argue all the time with my Ariel & The Bad Guy partner, Chael Sonnen, about this kind of thinking. Chael believes that if you are fighting in the UFC, you must fight the very best at all times. I believe that sometimes it's OK to take a step back and assess where you are as a fighter. Sometimes it's OK to look to build your confidence back up. To me, that's what this fight represents, and it seems like the first time in a very long time that McGregor is taking this approach.

And let me be very, very clear: Cerrone is no scrub. He's no cupcake. He's no tomato can. Quite frankly, I think he has been disrespected quite a bit the past five or so days. He's a perpetual tough out who is on a two-fight losing streak and turns 37 in March. He is the perfect fight right now for McGregor.

Why? Because he is a big name with an aggressive style that McGregor matches up well against and who, let's be honest, has often faltered in the big fight. Yes, Cerrone is the winningest fighter in UFC history, but he has never been a champion in a major organization. He has never won the big one. And hey, for a guy who has never complained about a matchup even when some of them didn't make a whole lot of sense for his career, it's nice to see him get this money fight.

A win over him lets us know that McGregor is back. Get by the litmus test that is Donald Cerrone, and then we can talk about Jorge Masvidal or Diaz.

That leads me to the fight's weight class. The one thing I don't like about this fight is that it is happening at 170 pounds. I think McGregor is at his very best when he fights at 155. For what it's worth, I also think Cerrone is at his best at 155. I like to see fighters compete at their best weight.

I asked someone close to McGregor why this fight is happening at welterweight. The response? "Because he's a bad m-f-" (with a smiley face emoji).

The last time Conor McGregor was on top of the MMA world was Nov. 12, 2016, when he defeated Eddie Alvarez to become a two-division champion. Jeff Bottari/Zuffa LLC/Getty Images

That told me all I needed to know. Several months ago, UFC president Dana White said Masvidal was too big for McGregor. That bothered McGregor. I think White knew that would bother McGregor, too, to be honest. Now fighting at 170 is part of his plan to prove wrong everyone who thinks Masvidal is too big. Win at 170 against Cerrone, get the body comfortable at that weight and then take on Masvidal or Diaz at 170. That's the game plan.

Because, remember, McGregor is planning to fight (and win) three times in 2020. Of course, a lot has to go his way for that to become a reality, but he has already mapped out what the perfect year would look like for him. Unlike most fighters trying to make comebacks, Conor is not taking this one fight at a time.

It starts with Cerrone, it continues with Masvidal (or Diaz), and it ends, he hopes, with the winner of Nurmagomedov vs. Ferguson for the lightweight title.

A lofty goal, right? The good news is we're about to find out very soon if it can come to fruition. Because if McGregor doesn't get by the litmus test that is Donald Cerrone, this comeback will be over before it started.

Fifth time's a charm

The other massive fight made official last week was Nurmagomedov vs. Ferguson. There isn't much more to say about this fight because we all agreed long ago that it was the only fight to make for both.

Amazingly, this is the fifth time the UFC has tried to book this matchup. Usually the promotion wouldn't go to the well so many times, but that speaks to how special this fight is. My only gripe is that it was made public four-and-a-half months before the April 18 fight night. That seems like you're asking for the dreaded MMA injury bug to ruin things again.

But I was told that the UFC is eager to get the 2020 first-quarter main events set by Dec. 13 because they are planning one of those big news conferences the night before UFC 245. Hence the rush. Fair enough.

Bring on the new year

Speaking of the first quarter of 2020, if the announced and proposed fights stay intact, it might be one of the best periods in recent memory, as far as pay-per-view main events and co-main events are concerned. Take a look:

Jan. 18: McGregor vs. Cerrone

Feb. 8: Jon Jones vs. Dominick Reyes and Valentina Shevchenko vs. Katlyn Chookagian

March 7: Israel Adesanya vs. Yoel Romero (maybe) and Zhang Weili vs. Joanna Jedrzejczyk

April 18: Nurmagomedov vs. Ferguson

It's great to see Joanna Jedrzejczyk rejuvenated and focused again, going for gold one more time. Tom Szczerbowski/USA Today Sports

Pretty great, right?

In addition to the fights we already discussed, I love what Zhang vs. Jedrzejczyk represents. The new champ needs to get by the former face of the division to properly start her reign. And who saw this coming from Jedrzejczyk after she lost to Rose Namajunas twice in strawweight title bouts and to Shevchenko at 125 pounds? It's great to see her rejuvenated and focused again after a tumultuous personal and professional stretch in her life, going for gold perhaps one last time.

Gamebred TV

It seems like Jorge Masvidal has seen and done it all this year -- except for TV color analyst work. Well, that changes this weekend. I'm told that Masvidal will be the "third man in the booth" for Combate Americas' first pay-per-view on Saturday, working alongside Max Bretos and Julianna Peña Masvidal calling Tito Ortiz vs. Alberto El Patron. It's so wacky it works.

ESPN Daily podcast Monday through Friday, host Pablo Torre brings you an inside look at the most interesting stories at ESPN, as told by the top reporters and insiders on the planet. Listen

Welcome back

Did you miss the UFC during its two-week break? I did. Imagine how much more you'd miss the fights after, say, a two-month break (but that's a topic for a different day). I'm intrigued by this weekend's Alistair Overeem vs. Jairzinho Rozenstruik main event because it seems like a potential passing of the torch. If Rozenstruik wins, how about the idea of him fighting Francis Ngannou, a fight he called for last week on the show? Fun.

Saturday's card in Washington, D.C., is sprinkled with intriguing fights featuring a few up-and-comers such as Bryce Mitchell, Song Yadong, Aspen Ladd (curious to see how she rebounds from her first loss) and Cynthia Calvillo. Plus, Matt Wiman is fighting, and that always gets me excited.

Hear and there

I can't believe Holly Holm isn't fighting on the New Mexico card in February. That is very disappointing. Instead, she meets Raquel Pennington a month earlier at UFC 246 in Las Vegas. That fight would have been a perfect main event for Feb. 15. ... But I think Corey Anderson vs. Jan Blachowicz, which is the main event for that Feb. 15 card outside Albuquerque, makes a lot of sense from a light heavyweight rankings standpoint. ... Sounds like we are getting closer to a Tyron Woodley vs. Leon Edwards fight in the first quarter of 2020 as well. ... Love the Paul Felder vs. Dan Hooker booking Feb. 23 in New Zealand. Perfect matchmaking. ... If you've never seen a KSW card, watch the Polish promotion's event this Saturday. They know how to put on a fun show, and the main event -- Scott Askham vs. Mamed Khalidov -- is a good one. ... Looking forward to seeing everyone at the second Helwani Road Show on Dec. 13 in Las Vegas. It's going to be a great time.