Eminem reportedly tested fellow rapper Kendrick Lamar to see if the latter really wrote his own material.

Eminem and Lamar have become two of the most celebrated rappers in the music industry, but the real Slim Shady wanted to see for himself if the rumors were true about Lamar's skills.

Fellow musician Ed Sheeran told a story about this on Zach Sang's radio show, a story he heard from producer Rick Rubin.

"Eminem heard that Kendrick Lamar was the best rapper and he invited him to the studio to get him on a song," Sheeran said. "He arrived, and Kendrick came with all his mates and Eminem said, 'I just want you in the studio, just you on your own and then my engineer is gonna come in and then record you doing it, but your mates aren't allowed in.' And then, Kendrick did it and wrote a sick verse. And then everyone came in to listen to it and Eminem said that he did it to test Kendrick, because he thought he had a ghostwriter. And he then realized that he didn't, and then claimed he was the best, which is kinda cool, I think."

Eminem and Lamar collaborated on the very catchy song "Love Game", which is featured on 2013's The Marshall Mathers LP 2.

Meanwhile, rumors continue to swirl that Eminem is releasing his ninth studio album in 2017. The rapper confirmed back in October that he was working on his new album, while releasing a new freestyle called "Campaign Speech". There were rumors that his new album would be called Success and feature collaborations with the likes of Adele, Kid Cudi, The Weeknd, Chance the Rapper, Mastein Bennett and Vince Staples. However, Eminem and his team have not confirmed this.

In the mean time, fans will have to continue listening to his first eight albums and his contributions to such movies as Southpaw.